Spamdexing is any of various methods to manipulate the relevancy or prominence of resources indexed by a search engine, usually in a manner inconsistent with the purpose of the indexing system. It is a form of search engine optimization. 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.
The rise of spamdexing in the mid-1990s made the leading search engines of the time less useful, and 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 decade, where it remains. Although it has not been rendered useless by spamdexing, Google has not been immune to more sophisticated methods either. 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 to the term spamdexing is by Eric Convey in his article "Porn sneaks way back on Web," The Boston Herald, May 22, 1996, where he said:
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 spam and link spam.