Malware-crossfire

hello, I do not speak English well because I'm Italian. but I wanted to say that when there was the update I had a malware that now makes me enter anymore. that says "file is canged: W [2007] L [2] crossfire.exe.
What should I do?
I have already installed and rienstallato but comes at a point, the malware
please write a clear so I can understand. thanks in advance.
use AVG.
thanks
date 27/5/11