Honestly? I have no idea. I got them all when I was using the virus open door program better known as Internet Explorer. Qhost I know how I got, it was on another friend's computer and it hooked onto a song she sent me. It's gone and it's never really a problem.
The Virtumod and the downloader.2655 aren't even listed in virus definitions so I have no idea what to do with em. I'd really like to know how I got em cause if they all came from my friend's machine, I'll be pissed.
ETA: Found out Virtumod is actually Trojan.Vundo which causes the Winfixer bullshit. So I think I've finally found a way to gtet rid of it. I still gotta figure out the downloader but at least I'll get this one off.
do you have a firewall running?
http://www.sophos.com/virusinfo/analyses/trojvirtumodd.html, is that the definition you may be looking for? This is installing more malware on your CPU, you may want to try scanning for spwyware or using hijack this and posting a log to see what you have going.