Spamdexing (also known as search spam, search engine spam, web spam or search engine poisoning) is the deliberate manipulation of search engine indexes. It involves a number of methods, such as repeating unrelated phrases, to manipulate the relevance or prominence of resources indexed in a manner inconsistent with the purpose of the indexing system.Some[who?] 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 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. An overarching term for using unsanctioned methods by search engines to have websites rank higher in those search engines is commonly called in the SEO industry as "Black Hat SEO." 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 (or term spam) and link spam. 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. Link spam Link spam is defined as links between pages that are present for reasons other than merit. Link spam takes advantage of link-based ranking algorithms, which gives websites higher rankings the more other highly ranked websites link to it. These techniques also aim at influencing other link-based ranking techniques such as the HITS algorithm.