Well, it looks like GUEST Just Amy comes closest to the prize. To be sure, as an English word, the plural of virus is viruses. In Latin, however, the word virus, meaning "poison", is one of those "-us" words which is not second declension masculine--which would make the plural viri--but fourth declension neuter. (Click here for boring details. So the plural is in fact virus. However, the author of that website missed one detail: the u in the plural form is actually a long vowel, which should be written with a macron (a little dash) over the letter, and pronounced like the "oo" in "boot", as opposed to the "oo" in "foot". (Not that anyone is really sure how the Romans pronounced their language, of course, since tape recorders were only used by a small religious sect in Herculaneum and were all lost in the eruption of Vesuvius...)

Aloha,
Marcus