Meaningless word used by people who are trying to write the plural of virus but never took Latin. In Latin, virus is a rare form of word and does not have an attributed plural form (i.e. no 'viri', and certainly no 'virii.') In English, the plural of virus is viruses. Look it up if you don't believe me.

Fictitious plural of the fictitious Latin word virius.

My ISP used to have "Virii are real" in big fat letters on its home page. I sent the owner an email saying, "No, they're not, but viruses are." He fixed it immediately. Must have felt quite embarassed, since it is not the type of error he was likely to make. I suspect he must have been answering a tech support call while he was typing the original, so he was distracted.

Ironically, if the word virius actually existed in Latin, it would mean something like manlier, which might indicate that virii is a "macho" mistake. But it doesn't, so it isn't.