Spamdexing (also known as search spam or search engine spam) involves a number of methods, such as repeating unrelated phrases, to manipulate the relevancy or prominence of resources indexed by a search engine, in a manner inconsistent with the purpose of the indexing system."Word Spy - spamdexing" (definition), March 2003, webpage:WordSpy-spamdexing. Some consider it to be a part of search engine optimization, though there are many search engine optimization methods that improve the quality and appearance of the content of web sites and serve content useful to many users. Search engines use a variety of algorithms to determine relevancy ranking. Some of these include determining whether the search term appears in the META keywords tag, others whether the search term appears in the body text or URL of a web page. Many search engines check for instances of spamdexing and will remove suspect pages from their indexes. Also, people working for a search-engine organization can quickly block the results-listing from entire websites that use spamdexing, perhaps alerted by user complaints of false matches. The rise of spamdexing in the mid-1990s made the leading search engines of the time less useful.

The success of Google at both producing better search results and combating keyword spamming, through its reputation-based PageRank link analysis system, helped it become the dominant search site late in the 1990s. Although it has not been rendered useless by spamdexing, Google has not been immune to more sophisticated methods. Google bombing is another form of search engine result manipulation, which involves placing hyperlinks that directly affect the rank of other sites. Google first algorithmically combated Google bombing on January 25, 2007.

The earliest known reference

The problem arises when site operators load their Web pages with hundreds of extraneous terms so search engines will list them among legitimate addresses.

The process is called "spamdexing," a combination of spamming — the Internet term for sending users unsolicited information — and "indexing."

Common spamdexing techniques can be classified into two broad classes: content spamNtoulas (or term spam) and link spam.Gyöngyi 2005

Content spam

These techniques involve altering the logical view that a search engine has over the page's contents. They all aim at variants of the vector space model for information retrieval on text collections.

Keyword stuffing

This involves the calculated placement of keywords within a page to raise the keyword count, variety, and density of the page. This is useful to make a page appear to be relevant for a web crawler in a way that makes it more likely to be found. Example: A promoter of a Ponzi scheme wants to attract web surfers to a site where he advertises his scam. He places hidden text appropriate for a fan page of a popular music group on his page, hoping that the page will be listed as a fan site and receive many visits from music lovers. Older versions of indexing programs simply counted how often a keyword appeared, and used that to determine relevance levels. Most modern search engines have the ability to analyze a page for keyword stuffing and determine whether the frequency is consistent with other sites created specifically to attract search engine traffic. Also, large webpages are truncated, so that massive dictionary lists cannot be indexed on a single webpage.