Hi:

Protecting your computer from parasites these days requires more than just an AV program and firewall. You need
to modify your web-surfing habits, tighten up your IE browser security configuration, be careful with email
attachments, and use a number of anti-parasite programs (such as Spybot S&D, Ad-Aware SE, Spywareblaster).

Fortunately, this is not expensive, as all that is required is some education, and utilies that are mostly
available as freeware. For a good overview of this topic, see this article from Net-Integration: So, how did I get
infected in the first place?. It has links to all the recommended download sites.