This whole "viruses/virii" argument is so stupid. First off, there are the Latin speakers who will argue 37 different reasons why such a word would or would not exist. Then there are the people who insist that virus is simply an English word and takes English pluralization.
Here's how it works. Hacker slang (or jargon, as in the "Jargon file") allows for the Latinesque construction of plurals by replacing "us" with "i", or "um" with "a" (or Anglo-Saxonish pluralization like "vaxen" or Hebrewish pluralization by adding "-im". Is this grammatically correct Latin (or Middle English, or Hebrew)? It doesn't matter... it's a play on words. The only point is that it is consistent with similar words.
What I find incredibly annoying is that people insist on using the "ii" suffix even though there is no precedent in real Latin, fake Latin or anything in between, presumably because it looks cool, or they have heard the word "radii".
Anyhow, that's my rant, and I'm sticking to it.