I don't know how virus becomes virii, but in my mind, virii sounds like a plural of virus anyway. Or something high tech.

I once had a virus that changed your IM programs to display everyone as online... it was horrible and at the same time comforting. I'd never felt so loved in my life. All the 8 people on my msn were online at once

Oh, and I gotta agree quickly that those worms are quite crafty buggers