What's the plural of "virus"?

Some of us try to use a classical approach when pluralizing words taken directly from Latin - id est index becomes indices instead of indexes and minimum becomes minima instead of minimums. So how do we pluralize virus?

Well, etymologically:

"Etymology: a. L. virus slimy liquid, poison, offensive odour or taste."

So virus isn't really countable. At the end of the day, viruses is kind of okay to use, but it's probably most correct to say virus for both singular and plural.