Posted by: Anonymous Coward
on January 27, 2005 07:00 PM
Virus comes from the latin word meaning slime. It's in a class of words for which there is no plural (slime is just slime and it never occurred to anyone that you would want to count 1 slime, 2 slimes, etc).
Even were you to use the wrong latin rule for making a plural, you would get virus -> viri. You wouldn't ever go -us (singular) to -ii (plural). Gladius, a sword, does have a plural gladii, though note the extra i in the singular form (-ius to -ii).
There is no "virii" that gets special treatment in medical or computer terminology.
All that's left is to use the English rule for forming the plural.