White hat versus black hat versus gray hat

SEO techniques are classified by some into two broad categories: techniques that search engines recommend as part of good design and those techniques that search engines do not approve of and attempt to minimize the effect of, referred to as spamdexing. Some industry commentators classify these methods, and the practitioners who employ them, as either white hat SEO, or black hat SEO.[29] 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.[30]
An SEO technique is considered white hat if it conforms to the search engines' guidelines and involves no deception. As the search engine guidelines[31][17][18][19] 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,[32] 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. Other black hat SEO tactics include keyword stuffing, doorway pages, redirects, duplicate sites, and interlinking, among others.[33]
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.
One infamous example was the February 2006 Google removal of both BMW Germany and Ricoh Germany for use of deceptive practices.[34] Both companies, however, quickly apologized, fixed the offending pages, and were restored to Google's list.[35]
Some techniques once considered white hat are now more often classified as gray hat.[citation needed] Gray hat SEO includes doing things like publishing duplicate content, creating multiple, identical sites, or less comprehensive or widespread artificial linking schemes. Gray hat SEO is similar in some ways to white hat SEO, but takes the optimizations further, possibly introducing some amount of unrelated content. Essentially, gray hat SEO includes things that are discouraged or could potentially result in a penalty, but that are very commonly done and are not explicitly forbidden to the same extent that black hat SEO technique are. Penalties for gray hat sites may be less severe than for black hat sites, tending more towards link devaluation rather than outright site banning.[36]