are you using the newest version of AIM? If so then it is unstable and will lock up your computer sometimes. Someone could be bombing/nuking you, does it happen all of the time? or only from certain people?
Do you know what virii/Trojans you had? some may require deeper cleaning.
check the following location in the registry for things that look out of place.
HKEY_LOCAL_MACHINE_/Software/Microsoft/Windows/Current Version/RunOnce or all of the other Run keys.
Look for out of place programs.
