The virus jumps to random terminals. You just open random terminals until you've hit the virus at 3 different terminals. Don't open the same terminal twice, they virus might not be there. This thing took me a long while to beat.
Actually, I think you'll find you CAN isolate it on one terminal (search the forum)!
you can isolate them to one console which makes it alot easier.i think you need a high science skill then do a speech check on the guy who gives you the job