Malwarebytes, from www.malwarebytes.org.
I have seen a lot of computers lately with the fake antivirus warnings, Antivirus 2009, subscribe and we will fix the infections, and fix your registry, but really we are the virus, and probably are looking to get paid to turn ourselves off for a while. It is bad. But malwarebytes seems to fix it pretty quickly, effectively and also for free. I love free stuff. I have found a few cases where the internet browser does not work after fixing, but that is also easily fixed, if you download winsockfix XP again, for free. Two more programs to keep on your USB key. If you watch this weeks Systm the guys show how to make a bootable USB key, using BartPE, and also ubuntu. Both are cool tools for fixing viruses as well.