There are a couple of interesting comments about this attack, first the Trojan/Virus is "unknown" Trojan activity is usually pretty spercific, i.e. mouse pointer going nuts, CD draw opening, applications starting in the back ground.

Also the fact NAV didn't detect (was the application updating correctly??).

You mention that you were running ZAPro, I know from experience that if and when an application request's access to the "net" the first time with ZA, a popup appears to ask if you want to give it access, for those bizzare things to have happened and for them to be caused by a trojan would mean that you gave the trojan access and weren't paying close attention, even so after you realised the issue you can turn on the "Internet Lock" in ZA, that would have stopped the erratic behaviour.

Finally I have just recently converted to LINUX, and I'm pleased to say the install and configuration went Sweet As !!!