Some of these spyware / malware programs can be VERY nasty.
My daughter had one (maybe two) on her laptop a few months ago called I think "AntiVirus 2009" and one other (I think her boyfriend downloaded them).
This really screwed up her laptop and it disabled our existing anti virus (AVG), changed settings in the Windows Security Centre, directed web traffic through their web site to stop us downloading any new other security software, stopped Google seach working, and when I managed to uninstall it, after reboot it just reinstalled itself again.
I know a lot about computers but just could not untangle it. In the end I had to completely reinstall Windows.
You can read a bit about it here to show you how nasty they are and what they can do.
http://en.wikipedia.org/wiki/Antivirus_2009