Virus problem

[MrFancypants]

Lately I've had some problems with a virus called W32/Stanit (also known as Gael or Tenga), I'm curious if one of you has an idea how I can protect my system from further infections.

About 3 weeks ago the virus was first noticed by my anti-virus program, it had infected an .exe file (patch for a game) I recently downloaded from a legit site and from there spread to a number of other .exe files before it was stopped. After removing the virus and checking the system a few times I thought I had dealt with it, but yesterday the same problem occured again, again after downloading a file (from the same website I got the first file from).

Now the strange part is this - I don't think the files I downloaded were infected, otherwise my anti-virus would have picked up on that when I ran them. The virus was only noticed later, when I deleted the files again (maybe it just starts with the latest .exe file it can find). Furthermore, the security hole in windows that this virus uses has been patched up years ago and my Win 7 has all the latest updates.

So how did I catch the virus? Maybe there is already some kind of malware installed that my virus scanner (Avira) and anti-spyware programs (Spybot) do not recognize?

[[+Glasius+]]

You can always upload the file in question to Jotti.
If you believe Avira isn't picking everything up, run Hijackthis and Wireshark to spot suspicious stuff.