How to Deal with Web Site Cloaking
Through a process of IP delivery called cloaking, a Web site detects who’s requesting to see a page and may show a different version to a search engine spider than to all other users. So the spider sees and indexes content that isn’t what you would see if you went to that URL. If the purpose of cloaking is to deceive search engines (which is the very definition of spam), there is a severe penalty.
Cloaking can be handled in a couple of ways, depending on if it's your site or another site:
On your own site. Don’t do it without consulting an ethical professional, and even then be cautious. If you have pages that detect the search engine spiders and change the page content as a result, you’re operating in dangerous waters that could get your site banished from the search engines.
On other sites. If you suspect that a competitor is using cloaking to gain an undeserved ranking in the search engines, you can compare their Web page to the version of the page that the search engine last cached (stored in their index).
Do a search that you know will include that Web page in the results set, and click the Cached link under the URL. This shows you the Web page as it last looked to the search engine. If you see entirely different content when you go to their live site, you’re probably looking at cloaking, and you can definitely report it as spam.
It’s no wonder the search engines hate it. Although not all forms of IP delivery are evil, deceptive cloaking is always wrong.