SEO techniques, devices or methods fall into two broad categories: those that search engines approve and recommend as appropriate to good design, and those, which simply do not. The search engines endeavor to reduce the impact of the techniques of which they disapprove by spamdexing. The methods, good or bad, have become popularly referred to as white hat SEO, and black hat SEO. White hats, are viewed positively and tend to produce longer lasting results, whereas black hats, viewed negatively, and similar to opportunist criminals who appreciate that their opportunity might be short-lived expect their site activity to be terminated either temporarily or permanently once they have been discovered.
White hat SEO involves no deception and conforms to the search engines' guidelines. It is an important distinction to note the search engine guidelines are not written as a series of commandments or rules. White hat SEO is not just about following guidelines, but is about ensuring that the content indexed by a search engine and subsequently ranked 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 allowing easy accessibility to the spiders, as opposed to attempted algorithm trickery. Although white hat SEO is similar in many ways to web development promoting accessibility, the two are not identical.
Black hat SEO contrives to increase ranking position in disapproved ways or involve deception such as using hidden text, possibly camouflaged within a text similar in color to the background or in an invisible div, or even positioned off screen. Giving a different page to that requested, depending on whether the request has come from a search engine or a human visitor is known as cloaking.
A search engine may penalize a site it discovers employing black hat techniques, through ranking reduction or relegation and sometimes elimination of their listing from their database completely. These penalties may be applied either by the search engines' algorithms automatically, or by a manual review of the site. One sensational example was when Google removed both BMW Germany and Ricoh Germany for using deceptive practices in February 2006. Both companies, however, quickly apologized, fixed the offending pages, and were restored to Google's list.
