For the cloaking used in Star Trek, see Cloaking (Star Trek).

Cloaking is a search engine optimization technique in which the content presented to the search engine spider is different than that presented to the users; this is done by either looking at the IP addresses of who is requesting the page, or by looking at the User-Agent HTTP header. While there are some legitimate uses for cloaking, like giving text to the search engines while giving Macromedia Flash to users (since search engines can't understand Flash), cloaking in most often used to try to trick the search engine into giving it a higher ranking than it would get without cloaking; it can also be used to trick search engine users into visiting a site that they ordinarily wouldn't, because the search engine's description of the site is different than the site's actual contents. For this reason, sites that are discovered to be using cloaking are permanently banned by most search engines.

A similar technique is also used on the Open Directory Project web directory. It differs in several ways from search engine cloaking:

  • It is intended to fool human editors, rather than computer search engine spiders.
  • The decision to cloak or not is based upon the HTTP referer, which tells the URL of the page on which a user clicked a link to get to the page. Some cloakers will give the fake page to anyone who comes from a web directory website, since directory editors will usually examine sites by clicking on links that appear on a directory webpage. Other cloakers give the fake page to everyone except those coming from a major search engine; this makes it harder to detect cloaking, while not costing them many visitors, since most people find websites by using a search engine.

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