I'm having trouble getting rid of a virus on my machine. The Avast scanner catches it everyday and deletes it, but it seems to keep coming back. I suspect it's using the Windows Update function to reinstall itself. I keep getting a pop-up from WinXP telling me new updates are ready to install. The machine does not ask to restart afterwards however, like it normally does. Shortly afterwards Avast catches this Win32:Spybot-z worm on my computer. I'm pretty sure I caught this virus from some program I installed off the internet.
Question: How do I get rid of this Virus once and for all?
PS. I searched for answers all over the internet and couldn't find anything. If anyone can help it would be greatly appreciated.