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8 Types of Bad Links to Avoid

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8 Types of Bad Links to Avoid

Have you ever wondered why your website isn’t ranking despite having quality content? Well, it could be because of the links you’ve been building.

In the world of SEO, links are a crucial ranking factor. With that comes a temptation for many website owners and marketers to resort to manipulative tactics to acquire links, which can lead to link spam.

This harmful practice can result in penalties from search engines, losing you both traffic and revenue. To avoid being penalized by search engines, it’s crucial to be familiar with the various types of bad links that fall under the umbrella of link spam.

In this article, we’ll provide you with the lowdown on link spam and eight types of bad links you should avoid at all costs.

Bad links are those that violate Google’s spam policies. In Google’s words, if the links are intended to manipulate rankings in Google Search results, they may be considered link spam. 

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Bad links mainly fall into two categories: (1) spammy, waste-of-time links and (2) those that are potentially dangerous to your site.

Why are bad links a problem?

Bad links can trigger a Google penalty, which means a significant drop in rankings and organic traffic. Your site may even be removed from the search results altogether:

Sites that violate our policies may rank lower in results or not appear in results at all.

But even if Google doesn’t penalize you, bad links are often a waste of time and money because many have no positive impact on rankings or traffic.

When to take action

Google has consistently said it’s very good at identifying and discounting spam links algorithmically. Therefore, you do not need to worry about finding and removing every single bad link.

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Google’s disavow tool allows you to discount links to avoid link-based penalties. But this tool can be incredibly damaging to your site, especially if you do not know what you are doing. 

Warning from Google's disavow tool

You shouldn’t disavow links haphazardly because you risk disavowing links that are actually helping you to rank. Just because you think a link is spammy doesn’t mean Google does.

With that in mind, there are only two instances where you should worry about bad links:

  • If you have received a manual action against your site for unnatural links.
  • If you know (or strongly suspect) a site has previously participated in shady link building.

Recently purchased a site or taken over the SEO of a site for a new client? If you know (or strongly suspect) those previously responsible actively participated in shady link building—such as PBNs—then it’s time to clean house. 

So what types of links are considered link spam?

Link spam definition

From Google’s definition of link spam, it could be argued that any link you land from link building is effectively link spam. After all, you are actively looking to acquire backlinks to improve your rankings in the search engine results pages (SERPs). 

So doesn’t that mean you are trying to manipulate rankings? 65% of SEOs agree.

But this is probably not what Google means. In fact, Google legend John Mueller has even previously praised quality link building acquisition methods like digital PR, stating they are just as crucial as tech SEO.

The examples Google gives of link spam are all things that most of us would consider crafty tactics that make the web a worse place. So these are basically what Google doesn’t want to see and those that you should avoid. 

Let’s look at some examples:

Types of bad links

1. PBNs

Private blog networks (PBNs) are made up of many websites you own linked together to manipulate search engine rankings.

How PBNs work

These link networks can be massive and mean building multiple topically relevant sites solely to link to one another. They’re designed to give the impression that links have been “earned” to create trust signals artificially. 

Why should you avoid these types of links?

If Google doesn’t catch you, then yes, PBNs can work and move the needle. The problem is that it’s hard to build an “undetectable” PBN unless you’re an experienced spammer. 

A truly sophisticated PBN needs to look and act like a real website, with genuine content and regular posting. It also needs to have different ownership, domain, and hosting providers to avoid being detected. 

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Quite honestly, if you are going to put that much work in, you may as well spend that time and effort on quality link building instead.

How to check if you have any

PBNs can be difficult to detect. However, if you suspect a website you just took over previously used PBNs to build links, then there’ll likely be some key giveaways.

One big one is websites that are all hosted on the same network, meaning they are all coming from the same IP address. 

With Ahrefs’ Site Explorer, you can find if multiple sites are linking to you from the same IP address with the Referring IPs report. 

Links by referring IP, via Ahrefs' Site Explorer

It’s important to say that just because multiple sites are on the same IP alone doesn’t confirm that sites are part of a PBN. They can be using the same hosting service (the examples above are all using Cloudflare).

However, if the websites also have these:

  • Little to no organic traffic 
  • Little content/no keywords
  • Links to each other
  • Spammy appearance and/or default themes

Then they can be key indicators of a PBN.

2. Paid links

Paid links are where you “buy or sell links for ranking purposes.” It’s important to mention that this doesn’t just include buying links for money. Exchanging links for goods or services or even buying a bloke a pint in return for a link all qualify as paid links.

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However, not all paid links are a problem as long as they have the right attributes. Google even states:

Google does understand that buying and selling links is a normal part of the economy of the web for advertising and sponsorship purposes.

However, any link that falls under those examples should have either a “nofollow” or “sponsored” attribute. 

Why should you avoid these types of links?

If you buy links from a site or one of the many “dear sir club” link builders, you’re going to get very little value from those links. 

Offer message about link building services

The reason is they will sell these to anyone. This makes the site an absolute spam fest and completely dilutes any link equity you could acquire. It also means these links are worthless at best and, at worst, could land you with a penalty. 

How to check if you have any

From my experience, it’s often easy to identify these links based on the anchor text. Most paid links will use exact match anchors and, on top of that, they are usually from low-quality sites with poor content.

Using Site Explorer, you can see all of the links to your site, including the anchor text. 

Example of an anchor text, via Ahrefs' Site Explorer

Of course, not every link with an exact match anchor will be a paid link. But you can get an idea of the quality from the URL of the linking site and the domain traffic. If these aren’t looking good, you can click through and check out the page directly. 

You don’t necessarily need to worry about removing these but, rather, avoid acquiring paid links in the first place. 

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3. Hacked links

Hacked links involve someone gaining access to a site and inserting content into existing pages. This means that search engines can see it. But as this is done within an existing page, it is often harder for website owners to detect. 

Why should you avoid these types of links?

Hacked links are completely unethical. Yet unfortunately, they still exist. These don’t fall specifically under link spam but under Google’s general spam policies

Google's hacked content policy

If you have links pointing to your site that were placed by hacking, the owner of the hacked website can report your site to Google and to your domain and hosting provider, resulting in your site being taken down. 

Hacking is also illegal in many countries, including the U.S. (under the Computer Fraud and Abuse Act) and in the U.K. (Computer Misuse Act 1990). 

Adding hacked links could be considered “hacking for notoriety” in order to appear as an authority on a particular topic which, in most cases, is illegal. 

How to check if you have any

There are instances of website owners paying link building agencies for guest posting services only to find the links they’ve acquired are indeed hacked after the hacked website has reported them. 

Unfortunately, there aren’t many ways to ensure that a link to your site was placed knowingly by the referring site. The best course of action is to be proactive and ensure that you either take charge of all link building activities yourself or use a reputable link building provider. 

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4. Hidden links

Hidden links are another thing that falls under Google’s general spam policies and is, again, totally unethical. 

These types of links can be done in many different ways:

  • Using white text on a white background
  • Hiding text behind an image
  • Using CSS to position text off-screen
  • Setting the font size or opacity to 0
  • Hiding a link by only linking one small character (for example, a hyphen in the middle of a paragraph)

Why should you avoid these types of links?

Like hacked links, these can be done without either the website owner or the linking site having any knowledge of these link placements but can land both sites with a Google penalty.

Unfortunately, I have personally worked with clients who have had this happen to them. In this instance, a link building agency they have previously worked with has had access to their site and placed hidden links to all their other clients’ websites, using them like a PBN. 

Hidden links example
An example of multiple hidden links placed in the footer of a website.

How to check if you have any

These links can be difficult to detect unless you already have a suspicion that they exist. 

I’ve found that one of the best ways to identify these links is by looking at the anchors and surrounding text. 

Usually, the link will have a very specific anchor, e.g., “we buy houses” for a realtor site. However, this will be surrounded by other random specific anchors and usually from a referring page that has no relevance to your own.

Here is an example from the Backlinks report in Site Explorer:

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Hidden link found using Ahrefs' Site Explorer

The above image shows a link with the anchor “we buy houses easley.” However, this is clearly surrounded by other keywords, which are also most likely anchor texts to other sites (policy solver, kw white label seo, etc.). 

These links also come from a website about Japanese shoguns with no topical relevance. 

This is enough to cause suspicion, so we should click through to the website and check if we can clearly see the links. 

In this case, no external links are visible on the page. However, with Ahrefs’ SEO Toolbar, you can see there are more than 50 similar outgoing links hidden on the page.

Outgoing links found using Ahrefs' SEO Toolbar

5. Link exchanges

Link exchanges or reciprocal linking is when two sites agree to exchange links with each other. Although link exchanges generally aren’t against Google’s guidelines, “excessive link exchanges” and “partner pages exclusively for the sake of cross-linking” are.

Why should you avoid these types of links?

Reciprocal link building happens naturally on the web all of the time (study). After all, it makes sense that you talk about other sites in your niche, and they talk about you.

Bar graph showing how common reciprocal links are

Linking out is also a great way to get the attention of other high-quality sites in your niche. If they return the favor by linking back in the future, then that’s definitely going to help your site.

But if you are going around contacting hundreds of sites and asking to exchange links, then that’s eventually going to cause you some harm.

Therefore, there is a fine line with this one. You must tread carefully not to be perceived as participating in any link exchange schemes. 

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How to check if you have any

You can see if you have multiple domains that have both outgoing and incoming links from your domain with the help of Site Explorer and Google Sheets. 

In Site Explorer, head over to Backlinks profile > Referring domains and export all of the data. Then head over to Outgoing links > Outgoing links report and, again, export the data. 

Referring domains report, via Ahrefs' Site Explorer

Add all of the exported data into a Google Sheet and look for duplicate domains. You can use a Google add-on like Remove Duplicates. This will highlight any duplicate domains so you can see which domains you have links both to and from.

Note that the key here is excessive link exchanges. Having a handful of reciprocal links isn’t going to send out red flags. However, if you have 30 or 40 (or more) reciprocal links to a single site, you may need to look at dialing those down.

6. Automated link building

Automated link building is where you use tools to build links at scale to your website with the touch of a button. 

Usually, these are in the form of tiered links. This means that you build links directly to your site (Tier 1) and then build additional links to the sites linking to yours (Tier 2, Tier 3, etc.). 

Flowchart showing how tiered link building works

Mostly, these automated programs build spammy links from poor-quality web 2.0 blog sites (yes, they’re really still a thing) and pile on some social signals for good measure. 

Why should you avoid these types of links?

Not only will the links these tools build do absolutely nothing for your site, but they are also clearly defined under Google’s link spam policy. If detected, these will likely land you with a penalty.

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Often, these types of links are offered as very cheap link building services on platforms like Fiverr, usually advertised as things like “foundation links.” You should avoid these services at all costs, as they are even more risky when you are not in control of the automation process. 

Example of "foundation links" service

How to check if you have any

These are often easy to spot as, usually, there are a mass of different referring domains linking to your site all with the same (or very similar) titles and anchor text. 

Automated link building example

Again, these aren’t really something to worry about removing. These spammy links are easily identified and ignored by Google. They are simply better to avoid in the first place, as they won’t do anything for your site.

7. Forum and comment spam

Forum spamming is another link building tactic where someone posts their website’s link in forums. Comment spam is where a person (or bot) leaves an irrelevant comment on a website with a link.

Why should you avoid these types of links?

There are two ways to spam forums. First, you can simply create multiple profiles and put your link in there. Secondly, you can place links in actual forum posts, either in the signature or in the body of the post.

The only way links should be used in forums is if they advise someone of something as part of a discussion.

Links in a forum comment
An example of how links should be used in forums.

If you run a WordPress blog, you’re probably already familiar with comment spam:

Example of comment spam

Comment spam blasts rely on the fact that:

  • Many sites allow comments to be posted without moderation.
  • Others just simply let spam comments slip through the net.

And that happens a lot…

Same comment spam found on multiple websites

Multiple sites with the same comment leave a pretty clear footprint of suspicious links for Google to pick up on and happily penalize. 

Both forum and comment spam violate Google’s quality guidelines and can lead to a penalty.

How to check if you have any

In honesty, I wouldn’t even waste time checking these. If you have links from comment spam, Google will likely automatically discount them. It’s more important to avoid acquiring them in the first place.

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8. Low-quality directories

Creating profiles on high-quality directory sites like Crunchbase is a great way to build an online presence for your business. However, when you start building these at scale on low-quality sites, it becomes spammy.

Why should you avoid these types of links?

It’s easy to fall into a trap with this one, especially for new business owners. Of course, you want to get your name out there, but this is all about quality over quantity. That’s why it is especially important to avoid link building services that do this at scale.

Example of "spam directories" service

This kind of low-quality, bulk-directory submission hasn’t worked for at least 15 years. These days, a forum blast such as this is likely to get your site penalized. 

So stick to well-known directory sites and avoid low-quality ones that will do nothing for your business and simply waste your time. 

How to check if you have any

You can usually spot directory links pretty quickly in Ahrefs’ free backlink checker, as the title of the referring page will most likely include your business name. 

Again, I wouldn’t worry too much about checking to see if you have these; simply avoid them in the first place. 

Final thoughts

A healthy backlink profile with high-quality links is an incredibly important aspect of SEO. Ensuring you use white-hat link building techniques and avoid actively acquiring bad links is key to preventing you from being penalized by Google.

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But it’s also important not to be too reactive when dealing with link spam. Basically, if you’ve already received a manual action, then you need to perform a link audit and use the disavow tool to remove any suspect links. But if you haven’t, it’s better to be proactive and try to avoid bad backlinks in the first place.

If you want to learn how to build awesome links the right way, check out our advanced link building course.

Got questions? Ping me on Twitter.



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How to Revive an Old Blog Article for SEO

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Step-by-Step: How to Optimize Old Blog Posts for SEO

Quick question: What do you typically do with your old blog posts? Most likely, the answer is: Not much.

If that’s the case, you’re not alone. Many of us in SEO and content marketing tend to focus on continuously creating new content, rather than leveraging our existing blog posts.

However, here’s the reality—Google is becoming increasingly sophisticated in evaluating content quality, and we need to adapt accordingly. Just as it’s easier to encourage existing customers to make repeat purchases, updating old content on your website is a more efficient and sustainable strategy in the long run.

Ways to Optimize Older Content 

Some of your old content might not be optimized for SEO very well, rank for irrelevant keywords, or drive no traffic at all. If the quality is still decent, however, you should be able to optimize it properly with little effort. 

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Refresh Content 

If your blog post contains a specific year or mentions current events, it may become outdated over time. If the rest of the content is still relevant (like if it’s targeting an evergreen topic), simply updating the date might be all you need to do.

Rewrite Old Blog Posts 

When the content quality is low (you might have greatly improved your writing skills since you’ve written the post) but the potential is still there, there’s not much you can do apart from rewriting an old blog post completely. 

This is not a waste—you’re saving time on brainstorming since the basic structure is already in place. Now, focus on improving the quality.

Delete Old Blog Posts 

You might find a blog post that just seems unusable. Should you delete your old content? It depends. If it’s completely outdated, of low quality, and irrelevant to any valuable keywords for your website, it’s better to remove it. 

Once you decide to delete the post, don’t forget to set up a 301 redirect to a related post or page, or to your homepage.

Promote Old Blog Posts 

Sometimes all your content needs is a bit of promotion to start ranking and getting traffic again. Share it on your social media, link to it from a new post – do something to get it discoverable again to your audience. This can give it the boost it needs to attract organic links too.

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Which Blog Posts Should You Update?

Deciding when to update or rewrite blog posts is a decision that relies on one important thing: a content audit. 

Use your Google Analytics to find out which blog posts used to drive tons of traffic, but no longer have the same reach. You can also use Google Search Console to find out which of your blog posts have lost visibility in comparison to previous months. I have a guide on website analysis using Google Analytics and Google Search Console you can follow.

If you use keyword tracking tools like SE Ranking, you can also use the data it provides to come up with a list of blog posts that have dropped in the rankings. 

Make data-driven decisions to identify which blog posts would benefit from these updates – i.e., which ones still have the chance to recover their keyword rankings and organic traffic. 

With Google’s helpful content update, which emphasizes better user experiences, it’s crucial to ensure your content remains relevant, valuable, and up-to-date.

How To Update Old Blog Posts for SEO

Updating articles can be an involved process. Here are some tips and tactics to help you get it right.

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Author’s Note: I have a Comprehensive On-Page SEO Checklist you might also be interested in following while you’re doing your content audit.

Conduct New Keyword Research

Updating your post without any guide won’t get you far. Always do your keyword research to understand how users are searching for your given topic. 

Proper research can also show you relevant questions and sections that can be added to the blog post you’re updating or rewriting. Make sure to take a look at the People Also Ask (PAA) section that shows up when you search for your target keyword. Check out other websites like Answer The Public, Reddit, and Quora to see what users are looking for too. 

Look for New Ranking Opportunities

When trying to revive an old blog post for SEO, keep an eye out for new SEO opportunities (e.g., AI Overview, featured snippets, and related search terms) that didn’t exist when you first wrote your blog post. Some of these features can be targeted by the new content you will add to your post, if you write with the aim to be eligible for it. 

Rewrite Headlines and Meta Tags

If you want to attract new readers, consider updating your headlines and meta tags. 

Your headlines and meta tags should fulfill these three things:

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  1. Reflect the rewritten and new content you’ve added to the blog post.
  2. Be optimized for the new keywords it’s targeting (if any).
  3. Appeal to your target audience – who may have changed tastes from when the blog post was originally made. 

Remember that your meta tags in particular act like a brief advertisement for your blog post, since this is what the user first sees when your blog post is shown in the search results page. 

Take a look at your blog post’s click-through rate on Google Search Console – if it falls below 2%, it’s definitely time for new meta tags. 

Replace Outdated Information and Statistics

Updating blog content with current studies and statistics enhances the relevance and credibility of your post. By providing up-to-date information, you help your audience make better, well-informed decisions, while also showing that your content is trustworthy.

Tighten or Expand Ideas

Your old content might be too short to provide real value to users – or you might have rambled on and on in your post. It’s important to evaluate whether you need to make your content more concise, or if you need to elaborate more. 

Keep the following tips in mind as you refine your blog post’s ideas:

  • Evaluate Helpfulness: Measure how well your content addresses your readers’ pain points. Aim to follow the E-E-A-T model (Experience, Expertise, Authoritativeness, Trustworthiness).
  • Identify Missing Context: Consider whether your content needs more detail or clarification. View it from your audience’s perspective and ask if the information is complete, or if more information is needed.
  • Interview Experts: Speak with industry experts or thought leaders to get fresh insights. This will help support your writing, and provide unique points that enhance the value of your content.
  • Use Better Examples: Examples help simplify complex concepts. Add new examples or improve existing ones to strengthen your points.
  • Add New Sections if Needed: If your content lacks depth or misses a key point, add new sections to cover these areas more thoroughly.
  • Remove Fluff: Every sentence should contribute to the overall narrative. Eliminate unnecessary content to make your post more concise.
  • Revise Listicles: Update listicle items based on SEO recommendations and content quality. Add or remove headings to stay competitive with higher-ranking posts.

Improve Visuals and Other Media

No doubt that there are tons of old graphics and photos in your blog posts that can be improved with the tools we have today. Make sure all of the visuals used in your content are appealing and high quality. 

Update Internal and External Links

Are your internal and external links up to date? They need to be for your SEO and user experience. Outdated links can lead to broken pages or irrelevant content, frustrating readers and hurting your site’s performance.

You need to check for any broken links on your old blog posts, and update them ASAP. Updating your old blog posts can also lead to new opportunities to link internally to other blog posts and pages, which may not have been available when the post was originally published.

Optimize for Conversions

When updating content, the ultimate goal is often to increase conversions. However, your conversion goals may have changed over the years. 

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So here’s what you need to check in your updated blog post. First, does the call-to-action (CTA) still link to the products or services you want to promote? If not, update it to direct readers to the current solution or offer.

Second, consider where you can use different conversion strategies. Don’t just add a CTA at the end of the post. 

Last, make sure that the blog post leverages product-led content. It’s going to help you mention your products and services in a way that feels natural, without being too pushy. Being subtle can be a high ROI tactic for updated posts.

Key Takeaway

Reviving old blog articles for SEO is a powerful strategy that can breathe new life into your content and boost your website’s visibility. Instead of solely focusing on creating new posts, taking the time to refresh existing content can yield impressive results, both in terms of traffic and conversions. 

By implementing these strategies, you can transform old blog posts into valuable resources that attract new readers and retain existing ones. So, roll up your sleeves, dive into your archives, and start updating your content today—your audience and search rankings will thank you!

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How Compression Can Be Used To Detect Low Quality Pages

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Compression can be used by search engines to detect low-quality pages. Although not widely known, it's useful foundational knowledge for SEO.

The concept of Compressibility as a quality signal is not widely known, but SEOs should be aware of it. Search engines can use web page compressibility to identify duplicate pages, doorway pages with similar content, and pages with repetitive keywords, making it useful knowledge for SEO.

Although the following research paper demonstrates a successful use of on-page features for detecting spam, the deliberate lack of transparency by search engines makes it difficult to say with certainty if search engines are applying this or similar techniques.

What Is Compressibility?

In computing, compressibility refers to how much a file (data) can be reduced in size while retaining essential information, typically to maximize storage space or to allow more data to be transmitted over the Internet.

TL/DR Of Compression

Compression replaces repeated words and phrases with shorter references, reducing the file size by significant margins. Search engines typically compress indexed web pages to maximize storage space, reduce bandwidth, and improve retrieval speed, among other reasons.

This is a simplified explanation of how compression works:

  • Identify Patterns:
    A compression algorithm scans the text to find repeated words, patterns and phrases
  • Shorter Codes Take Up Less Space:
    The codes and symbols use less storage space then the original words and phrases, which results in a smaller file size.
  • Shorter References Use Less Bits:
    The “code” that essentially symbolizes the replaced words and phrases uses less data than the originals.

A bonus effect of using compression is that it can also be used to identify duplicate pages, doorway pages with similar content, and pages with repetitive keywords.

Research Paper About Detecting Spam

This research paper is significant because it was authored by distinguished computer scientists known for breakthroughs in AI, distributed computing, information retrieval, and other fields.

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Marc Najork

One of the co-authors of the research paper is Marc Najork, a prominent research scientist who currently holds the title of Distinguished Research Scientist at Google DeepMind. He’s a co-author of the papers for TW-BERT, has contributed research for increasing the accuracy of using implicit user feedback like clicks, and worked on creating improved AI-based information retrieval (DSI++: Updating Transformer Memory with New Documents), among many other major breakthroughs in information retrieval.

Dennis Fetterly

Another of the co-authors is Dennis Fetterly, currently a software engineer at Google. He is listed as a co-inventor in a patent for a ranking algorithm that uses links, and is known for his research in distributed computing and information retrieval.

Those are just two of the distinguished researchers listed as co-authors of the 2006 Microsoft research paper about identifying spam through on-page content features. Among the several on-page content features the research paper analyzes is compressibility, which they discovered can be used as a classifier for indicating that a web page is spammy.

Detecting Spam Web Pages Through Content Analysis

Although the research paper was authored in 2006, its findings remain relevant to today.

Then, as now, people attempted to rank hundreds or thousands of location-based web pages that were essentially duplicate content aside from city, region, or state names. Then, as now, SEOs often created web pages for search engines by excessively repeating keywords within titles, meta descriptions, headings, internal anchor text, and within the content to improve rankings.

Section 4.6 of the research paper explains:

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“Some search engines give higher weight to pages containing the query keywords several times. For example, for a given query term, a page that contains it ten times may be higher ranked than a page that contains it only once. To take advantage of such engines, some spam pages replicate their content several times in an attempt to rank higher.”

The research paper explains that search engines compress web pages and use the compressed version to reference the original web page. They note that excessive amounts of redundant words results in a higher level of compressibility. So they set about testing if there’s a correlation between a high level of compressibility and spam.

They write:

“Our approach in this section to locating redundant content within a page is to compress the page; to save space and disk time, search engines often compress web pages after indexing them, but before adding them to a page cache.

…We measure the redundancy of web pages by the compression ratio, the size of the uncompressed page divided by the size of the compressed page. We used GZIP …to compress pages, a fast and effective compression algorithm.”

High Compressibility Correlates To Spam

The results of the research showed that web pages with at least a compression ratio of 4.0 tended to be low quality web pages, spam. However, the highest rates of compressibility became less consistent because there were fewer data points, making it harder to interpret.

Figure 9: Prevalence of spam relative to compressibility of page.

The researchers concluded:

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“70% of all sampled pages with a compression ratio of at least 4.0 were judged to be spam.”

But they also discovered that using the compression ratio by itself still resulted in false positives, where non-spam pages were incorrectly identified as spam:

“The compression ratio heuristic described in Section 4.6 fared best, correctly identifying 660 (27.9%) of the spam pages in our collection, while misidentifying 2, 068 (12.0%) of all judged pages.

Using all of the aforementioned features, the classification accuracy after the ten-fold cross validation process is encouraging:

95.4% of our judged pages were classified correctly, while 4.6% were classified incorrectly.

More specifically, for the spam class 1, 940 out of the 2, 364 pages, were classified correctly. For the non-spam class, 14, 440 out of the 14,804 pages were classified correctly. Consequently, 788 pages were classified incorrectly.”

The next section describes an interesting discovery about how to increase the accuracy of using on-page signals for identifying spam.

Insight Into Quality Rankings

The research paper examined multiple on-page signals, including compressibility. They discovered that each individual signal (classifier) was able to find some spam but that relying on any one signal on its own resulted in flagging non-spam pages for spam, which are commonly referred to as false positive.

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The researchers made an important discovery that everyone interested in SEO should know, which is that using multiple classifiers increased the accuracy of detecting spam and decreased the likelihood of false positives. Just as important, the compressibility signal only identifies one kind of spam but not the full range of spam.

The takeaway is that compressibility is a good way to identify one kind of spam but there are other kinds of spam that aren’t caught with this one signal. Other kinds of spam were not caught with the compressibility signal.

This is the part that every SEO and publisher should be aware of:

“In the previous section, we presented a number of heuristics for assaying spam web pages. That is, we measured several characteristics of web pages, and found ranges of those characteristics which correlated with a page being spam. Nevertheless, when used individually, no technique uncovers most of the spam in our data set without flagging many non-spam pages as spam.

For example, considering the compression ratio heuristic described in Section 4.6, one of our most promising methods, the average probability of spam for ratios of 4.2 and higher is 72%. But only about 1.5% of all pages fall in this range. This number is far below the 13.8% of spam pages that we identified in our data set.”

So, even though compressibility was one of the better signals for identifying spam, it still was unable to uncover the full range of spam within the dataset the researchers used to test the signals.

Combining Multiple Signals

The above results indicated that individual signals of low quality are less accurate. So they tested using multiple signals. What they discovered was that combining multiple on-page signals for detecting spam resulted in a better accuracy rate with less pages misclassified as spam.

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The researchers explained that they tested the use of multiple signals:

“One way of combining our heuristic methods is to view the spam detection problem as a classification problem. In this case, we want to create a classification model (or classifier) which, given a web page, will use the page’s features jointly in order to (correctly, we hope) classify it in one of two classes: spam and non-spam.”

These are their conclusions about using multiple signals:

“We have studied various aspects of content-based spam on the web using a real-world data set from the MSNSearch crawler. We have presented a number of heuristic methods for detecting content based spam. Some of our spam detection methods are more effective than others, however when used in isolation our methods may not identify all of the spam pages. For this reason, we combined our spam-detection methods to create a highly accurate C4.5 classifier. Our classifier can correctly identify 86.2% of all spam pages, while flagging very few legitimate pages as spam.”

Key Insight:

Misidentifying “very few legitimate pages as spam” was a significant breakthrough. The important insight that everyone involved with SEO should take away from this is that one signal by itself can result in false positives. Using multiple signals increases the accuracy.

What this means is that SEO tests of isolated ranking or quality signals will not yield reliable results that can be trusted for making strategy or business decisions.

Takeaways

We don’t know for certain if compressibility is used at the search engines but it’s an easy to use signal that combined with others could be used to catch simple kinds of spam like thousands of city name doorway pages with similar content. Yet even if the search engines don’t use this signal, it does show how easy it is to catch that kind of search engine manipulation and that it’s something search engines are well able to handle today.

Here are the key points of this article to keep in mind:

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  • Doorway pages with duplicate content is easy to catch because they compress at a higher ratio than normal web pages.
  • Groups of web pages with a compression ratio above 4.0 were predominantly spam.
  • Negative quality signals used by themselves to catch spam can lead to false positives.
  • In this particular test, they discovered that on-page negative quality signals only catch specific types of spam.
  • When used alone, the compressibility signal only catches redundancy-type spam, fails to detect other forms of spam, and leads to false positives.
  • Combing quality signals improves spam detection accuracy and reduces false positives.
  • Search engines today have a higher accuracy of spam detection with the use of AI like Spam Brain.

Read the research paper, which is linked from the Google Scholar page of Marc Najork:

Detecting spam web pages through content analysis

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New Google Trends SEO Documentation

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Google publishes new documentation for how to use Google Trends for search marketing

Google Search Central published new documentation on Google Trends, explaining how to use it for search marketing. This guide serves as an easy to understand introduction for newcomers and a helpful refresher for experienced search marketers and publishers.

The new guide has six sections:

  1. About Google Trends
  2. Tutorial on monitoring trends
  3. How to do keyword research with the tool
  4. How to prioritize content with Trends data
  5. How to use Google Trends for competitor research
  6. How to use Google Trends for analyzing brand awareness and sentiment

The section about monitoring trends advises there are two kinds of rising trends, general and specific trends, which can be useful for developing content to publish on a site.

Using the Explore tool, you can leave the search box empty and view the current rising trends worldwide or use a drop down menu to focus on trends in a specific country. Users can further filter rising trends by time periods, categories and the type of search. The results show rising trends by topic and by keywords.

To search for specific trends users just need to enter the specific queries and then filter them by country, time, categories and type of search.

The section called Content Calendar describes how to use Google Trends to understand which content topics to prioritize.

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Google explains:

“Google Trends can be helpful not only to get ideas on what to write, but also to prioritize when to publish it. To help you better prioritize which topics to focus on, try to find seasonal trends in the data. With that information, you can plan ahead to have high quality content available on your site a little before people are searching for it, so that when they do, your content is ready for them.”

Read the new Google Trends documentation:

Get started with Google Trends

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