SEO techniques are considered white hat if they comply with search engine guidelines and do not involve deception. This is an important distinction to note since search engine guidelines are not written as a series of rules or precepts. White hat SEO is more than just following phone number thailand guidelines, it is about ensuring that the content that search engines index and subsequently rank is the same content that users will see. White hat advice is often summarized as creating content for users rather than search engines, and then making that content easily accessible to online "spider" algorithms, rather than trying to trick the algorithms into deviating from their intended purpose. White hat SEO is similar in many ways to web development that promotes accessibility, although the two are not the same.
Black hat SEO attempts to improve rankings in ways that search engines disapprove of or involve deception. One black hat technique is to use hidden text, either text that is a similar color to the background, placed in an invisible div, or placed off-screen. Another method displays different pages depending on whether the page is requested by a human visitor or a search engine, a technique called cloaking. Another type is sometimes used, gray hat SEO. This method is somewhere in between black hat and white hat methods, using methods that can avoid penalties for the site but do not provide the best content for users. Gray hat SEO focuses entirely on improving search engine rankings.
Search engines may penalize sites that use black hat or gray hat methods, either by lowering their rankings or removing their listings from their databases entirely. Such penalties can be applied automatically by the search engine's algorithm or through manual site audits. An example is when Google removed the websites of BMW Germany and Ricoh Germany in February 2006 for using deceptive practices. However, both companies quickly apologized, fixed the offending pages, and were restored to Google's search engine results pages.