The latest variants of the CoolWebSearch trojan are a little bit nasty and like all CWS variants are apparently mutating on a regular basis. It seems like they spend a real lot of time trying to find every nasty trick that can be pulled and then bundling it all together for our web-browsing pleasure.
Anyway it is typified by some large warning banner or other overtaking the desktop (hence 'DesktopHijack') and installation of various dubious Spyware/Virus removal programs. There are now some tools about to help automate it's removal. Although from experience I can tell you they may not completely solve your issues they should at least recover your PC to a usable state, you may need to delete the HOSTS file to further the process but it depends on what other crap you have accumulated.
- http://www.bleepingcomputer.com/files/reg/smitfraud.reg registry patch to remove many of the smitfraud modifications.
- http://www.spywareedge.net/tools/smitRem.zip Automated removal of Smitfraud earlier variant.
- http://www.intermute.com/spysubtract..._download.html the latest version of the CWS removal tool - now owned and maintained by Trend Micro.
- http://www.pandasoftware.com/product..._principal.htm Panda Antivirus online scan - Panda is very good.
There is a detailed listing of the earlier SmitFraud variants and what it does at Symantec