Doorway Pages and Cloaking Software
The reasons for cloaking are generally twofold: to protect pages from other search engine optimization (SEO) firms and to increase search engine ranking.
SEO firms spend a lot of time and money creating Web pages they hope will rank high in search engine inquiries; they want to protect their methods from other SEO companies. This makes it a ratings game, with higher search engine rankings taking priority over content. In theory, this will increase the number of visitors to the site, but increasing traffic doesn't necessarily result in an increase in Web site income. If a visitor finds something different on the Web page than that returned by the search engines, the chances are pretty good that the visitor will leave and not return.
In order to create pages that rank high with search engines, it's usually easier to concentrate on how it will "look" to the robot doing the indexing than to a human visitor. For this to work, a different page is presented to the human visitor.
Notice that in both of these scenarios the actual Web page — the one visible to a human visitor — has been hidden from the search engine robot.
Doorway Page Wizard is the top of the line cloaking software used by search engine optimization (SEO) professionals.