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Examples of Black Hat SEO

Here are some definitions of what Yahoo!, MSN Search and Google consider to be unacceptable SEO (aka spam). This list is not exhaustive. Some of these are discussed in more detail elsewhere.

Keyword, Anchor Text and Domain Name Stuffing
Using hidden text or links. These could be hidden in ALT tags of images or made the same color as the page background so as to appear invisible to the end user. Style Sheets (CSS Spam) can be used in an attempt to hide these manipulations from search engine's anti-spam filters.
Using techniques to artificially increase the number of links to your page, such as link farms or buying and selling links with the main aim of increasing rankings in results pages
Excessively cross-linking sites to inflate the apparent popularity
Cloaking, delivering different pages depending the IP address and/or agent who is requesting it
Doorway/Gateway/Jump Pages - pages designed as an entrance to a website, each one of them optimized for a different keyword but which have no real content. These automatically redirect the user to the main website. This tactic is heavily used by adult content sites. Often with a Javascript mouseover redirect that sends the user to the new page as soon as the cursor hovers over the page content
Duplicate Content. Identical or very similar pages that can be accessed from different URLs. Examples would be copies of the Open Directory Project listings or online books taken from Project Gutenberg. Someone could even steal the content of your website! Google has registered patent number: 6,658,423 aimed at detecting duplicates.
Auto-generated content of no value to the end user. The aim being to either target keywords or to create excessive internal links
Misuse or cyber-squatting of competitor domain names or name typos, for example: Microsofr.com
Spamming Forums and Weblogs (Blogs)
Excessive outbound links to websites that use high risk techniques or Spam
Hiding outbound-links either with Javascript or by redirecting to a gateway page blocked by a robots.txt file
Link Hoarding, getting as many inbound-links while giving out few outbound-links

Few of these tactics would get a site banned from an index on their own. It is more a pattern of abuse that will trigger penalties. Many of these techniques can be automatically detected by search engine robots when they index the site. Website owners using commercial search engine optimization services should watch out if these tactics are proposed for two reasons. Any business proposing unethical tactics may not be that ethical itself and the optimizations may get the clients banned. There are examples of both of these happening.

Some black-hat schemes are more subtle. In the section on PageRank we discuss how the global PageRank available to a site is equivalent to the total number of pages. The structure of a website can be used to distribute this ranking within the site. For example a hierarchies feed PageRank back to the top or home page of the site. It would be possible to construct a site where pages below the home page are interconnected and each has a connection to the home page. For a site with only 10 pages and no incoming links the home page has over 3 times the average PageRank of 1.0.

Figure 1: Homepage PageRank increased by site structure

This sort of structure is quite common for presentations and books that should be followed sequentially. Imagine a site with thousands of pages of content. The search engines warn against using automatically generated pages for exactly this reason. However content is freely available on the Web, an example would be the online books available as part of Project Gutenberg. Most of these are now out of copyright and Project Gutenberg puts very limited restrictions on redistribution. It would be feasible to create many pages of content in many different ways and it would be difficult for search engines to automatically classify this as duplicate content. The site structure, while giving a boost to pages at the top of the hierarchy would be in keeping with a book format. Unfortunately there is little new under the sun. If you think up a new SEO angle the chances are it has already been done. In the above example an SEO expert has created just such as classic literate site, it has a healthy PR6 and the owner makes a living from content targeted advertising.

Examples of Black Hat SEO

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