Link: http://cybernetnews.com/2008/10/28/adobe-photoshop-cs4-crack-keygen/

Well, if you went out and got yourself a copy of CS4 before this fix you have a year demo at least. If you waited you can now have an unlimited version.

Ingeniously someone came up with a way to get around this by modifying the operating system’s HOSTS file (available on both Mac and Windows) so that any requests to Adobe’s server’s never leave the comfort of your machine. If it can’t contact Adobe then it can’t deactivate the software.

I don't really know how ingenious it is - but if it works it works.