Hidden Javascript Redirect

The hidden javascript has been used on many occasions to fool search engines, it involves obfuscating the javascript code so that the redirect is not picked up by the serach engine spider so that different content is shown to the spider than to a human visitor. This technique is NOT recommended as once search engines discovered that it was happening they took measures against this practice.

Google's statement on Cloaking, Sneaky Javascript Redirects and Doorway Pages can be viewed by clicking the link. Bing makes a statement on Cloaking (including Hidden Redirects) here.