Types of SEO
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. Professional SEO consultants do not offer spamming and spamdexing techniques amongst the services that they provide to clients. Some industry commentators classify these methods, and the practitioners who utilize them, as either white hat SEO, or black hat SEO. Different hat colors do not necessarily imply differences in ethics as much as differences in business models. White hats tend to produce results that last a long time, whereas black hats anticipate that their sites will eventually be banned once the search engines discover what they are doing.
An SEO tactic, technique or method is considered white hat if it conforms to the search engines' guidelines and involves no deception. As the search engine guidelines 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 game the algorithm. White hat SEO is in many ways similar to web development that promotes accessibility,although the two are not identical.
Spamdexing / Black hat
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 redirects users from a page that is built for search engines to one that is more human friendly. A method that sends a user to a page that was different from the page the search engined ranked is black hat as a rule. The black hat practice of serving one version of a page to search engine spiders and another version to human visitors is called 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.
One infamous example was the February 2006 Google removal of both BMW Germany and Ricoh Germany for use of deceptive practices.Both companies, however, quickly apologized, fixed the offending pages, and were restored to Google's list.