Meta spam
Now consider meta spam. Meta data is data that describes a resource. Meta spam is data that mis-describes a resource or describes a resource incoherently in order to manipulate a search engine's relevancy calculations.
Think again about the humble ALT tag. Not only does it provide content for a HTML resource, it also provides a description of an image resource. In this description capacity, to mis-describe an image or to describe it incoherently (using, say, a stream of keywords instead of a descriptive sentence or phrase) is meta-spam. Perhaps the best examples of meta spam at present can be found in the <head> section of HTML pages. Remember, though, it’s only spam if it is done purely for search engine relevancy gain.
Meta spam is more abstract than content spam. Rather than discuss it in abstract terms, we will take some examples from HTML and XML/RDF in order to illustrate meta spam and where it differs from and crosses with content spam.
Generally, anything within the <head> section of an HTML document, or anything within the <body> section that describes another resource, can be subverted to deliver meta spam.
Examples of meta spam
The TITLE Tag
Location: <head> section of a HTML document
Example: <title>White Paper : The Classification of Search Engine Spam</title>
Search engines tend to place a lot of emphasis on the title tag in determining relevancy. Basically, if keywords occur in a page's title tag, the page is more likely to be seen as relevant to those keywords. The title of this document is "White Paper : The Classification of Search Engine Spam", which accurately describes (using terminology appropriate to the target audience) the contents of this document. If we had made the title of this document "Spammer's delight - click here to find out how to spam the search engines, SPAM, Spam, spam, ugly spam, obvious spam" then we would have a couple of problems. One, the title would mis-describe this page. Two, the title would be incoherent, yet it is designed for search engine users to see.
Caveat: the <title> tag has several functions beyond search engine listings. If an alternative use can justify using a particular title, then the title is not spam.
The META DESCRIPTION tag
Location: <head> section of a HTML document
Example: <meta name="Description" id="Description" content="The definitive guide to search engine spam." />
Everything said above about the title tag equally applies to the meta description tag. However, the caveat regarding alternative uses is not as strong. The title tag has many uses – the meta description tag is almost exclusively used by search engines.
The META KEYWORDS tag
Location: <head> section of a HTML document
Example: <meta name="Keywords" id="Keywords" content="spam classification search engine optimization optimisation ethical marketing marketer professional" />
Unlike the title and meta description tags, the meta keywords tag is not generally displayed to searchers. Therefore, it does not need to meet the "coherency" condition. In addition, the keywords tag was designed by search engines to assist search engines in determining relevancy. Therefore, it is our opinion that nothing in the keywords tag should be considered to be spam. Instead, the search engine should use the keywords tag either not at all or to guide keyword selection, but not to influence the relevancy calculations of those keywords.
Dublin Core Tags
Location: <head> section of a HTML document
Example: <meta name="DC.title" id="DC.title" content=" White Paper : The Classification of Search Engine Spam" />
The Dublin Core tags can be considered similarly to the meta tags already described.
XML/RDF Tags and Metadata
Location: XML/RDF files or streams or embedded in other Web resources
Example: <dc:title>White Paper : The Classification of Search Engine Spam</dc:title>
XML/RDF tags and metadata can be considered similarly to the meta tags already described. It is important to note that the use of XML/RDF will, in itself, not bring an end to search engine spam. It will simply provide an alternative spam channel. In fact, it could provide a greater opportunity for spam unless careful checks and balances, or contracts and conditions, are applied.
That concludes the discussion of types of search engine spam. The remainder of this document will consider issues such as links, redirection, agent delivery, IP delivery, cloaking, the role of the search engine and the role of the marketer.
Links
With link popularity taking on a greater importance in the calculation of relevancy, the spammer’s attention has turned to how to manipulate this factor. Link popularity has two components: the authority component (number of links from other resources to this resource) and the hub component (number of links from this resource to other resources).
Techniques such as link farms have been developed to subvert both the authority and hub components. What is a link farm?
Link farm
A network of pages on one or more Web sites, heavily cross-linked with each other, with the sole intention of improving the search engine ranking of those pages and sites.
How can link farm pages be distinguished from other pages? The means of the determination is beyond the scope of this document. Suffice it to say that it can be done (hint: draw Web graphs of some small link farms and look at the patterns that emerge).
Links can be used to deliver both types of search engine spam, i.e. both content spam and meta spam.