The advise you aleady got about not connecting to the Internet was good, but very hard for some of us.
I guess that I am one of a few that runs the Microsoft Windows Live One Care program. This has both an Anti-Virus and Firewall built in and some other more or less useful features. I was attracted to it by the fact that you can have up to 3 computers registered on one contract and I think it was only $50 / year.
I have been running it for about 9 months without any problems and on my editing box, I simply block the Internet connection in the Firewall for just about everything except Microsoft programs.
Just my 2 cents worth.
Bruce