White hat versus black hat
SEO techniques can be classified into two broad categories: techniques that search engines recommend as part of good design, and those techniques of which search engines do not approve. The search engines attempt to minimize the effect of the latter, among them
spamdexing. Some industry commentators have classified these methods, and the practitioners who employ them, as either
white hat SEO, or
black hat SEO.
[35] White hats tend to produce results that last a long time, whereas black hats anticipate that their sites may eventually be banned either temporarily or permanently once the search engines discover what they are doing.
[36]
An SEO technique is considered white hat if it conforms to the search engines' guidelines and involves no deception. As the search engine guidelines
[21][22][23][37] are not written as a series of rules or commandments, this is an important distinction to note. White hat SEO is not just about following guidelines, but is about ensuring that the content a search engine indexes and subsequently ranks is the same content a user will see. White hat advice is generally summed up as creating content for users, not for search engines, and then making that content easily accessible to the spiders, rather than attempting to trick the algorithm from its intended purpose. White hat SEO is in many ways similar to web development that promotes accessibility,
[38] although the two are not identical.
Black hat SEO attempts to improve rankings in ways that are disapproved of by the search engines, or involve deception. One black hat technique uses text that is hidden, either as text colored similar to the background, in an invisible
div, or positioned off screen. Another method gives a different page depending on whether the page is being requested by a human visitor or a search engine, a technique known as
cloaking.
Search engines may penalize sites they discover using black hat methods, either by reducing their rankings or eliminating their listings from their databases altogether. Such penalties can be applied either automatically by the search engines' algorithms, or by a manual site review. Infamous examples are the February 2006 Google removal of both
BMW Germany and
Ricoh Germany for use of deceptive practices.
[39] and the April 2006 removal of the PPC Agency BigMouthMedia.
[40] All three companies, however, quickly apologized, fixed the offending pages, and were restored to Google's list.
[41]
Many Web applications employ back-end systems that dynamically modify page content (both visible and meta-data) and are designed to increase page relevance to search engines based upon how past visitors reached the original page. This dynamic search engine optimization and tuning process can be (and has been) abused by criminals in the past. Exploitation of Web applications that dynamically alter themselves can be
poisoned.
[42]
