Trillian: you set up your logins/name for each messenger programme you want to use, then sorts it all out for you there. People are colour coded as to which system they're on, but you don't really have to know that - you just click on the person you want to chat to and get on with it, without worrying about which network you are on.
You don't get full functionality, but a large proportion - I've managed multiple people chats on MSN quite happily even though I'm not using that software. I see the picture links etc.
Primarily, I use it because I have friends on ICQ, AIM and MSN and there was no way I was going to run 3 separate messenger programmes at once. But the security issues are also a bonus
Incidentally, from what I read last night, this particular virus is a bit like nits () in that it can reside in several files - if you miss one, it can then reinfect the entire PC again. Strongly recommend you do a virus sweep every day for a few days just to double check you got everything.