http://lysy2.archives.nd.edu/cgi-bin/WORDS.EXE?virus
In English the plural is viruses.
In English, there's never a reason to use anything other than "viruses".
Actually, virus is a "mass noun" (uncountable) and has no plural. If it ever had a nominative plural it would be vira, and out of anything, viri is its genitive singular.
No, that's the Latin plural of vir; viri means "men" not "poisons" ("virus" means "poison" in Latin.) [1]
http://www.google.com/#q=translate+viri+from+latin+to+englis...
If one person is ignorant in one domain, that doesn't mean that person doesn't excel in another domain. Stupidity is relative.
E.g. my father can't use a computer and thinks his computer is broken whenever he has minor problems with it. On the other hand he has a perfect track record in managing government institutions and the family's business and he's also extremely good at handling money and being a cheap bastard. He never learned to use a computer simply because he can delegate such tasks to his subordinates (or me).
And yet you've placed him in the bucket of people with more money than brains, simply because somebody on this planet sold his computer because it was virused.