If you said “virii,” bzzzzzzzzt!
The correct answer is “viruses.”
I’ve won several rounds of drinks and at least one dinner with this one. Here’s a tip for those who like to make bets: People who insist on saying “virii” are often wine geeks as well, so this is a good topic to bring up when perusing the wine list. If you can get the person across the table to pay for an $80 bottle of wine by winning this bet, it will taste even better.
Ed Bott 
Finally someone who agrees with me on this one! Irrespective of the Latin root of the word (as to which there has been considerable debate: http://www.linuxmafia.com/~rick/faq/plural-of-virus.html), the plural has always been “viruses”. As a one-time Latin scholar, it always amuses me when folks attempt to appear learned by using what they think are Latin words, when in fact they are not!
That’s esp. good to know the next time I’m on Jeopardy with Ken Jennings! š
Actually, the plural of virus is “Windows.”
Heh. Sorry. Couldn’t resist.