Het meervoud van virus (in het engels) is...:

Except that there is no basis for virii being the plural of virus in Latin whatsoever. The plural of murus (wall) is muri. The plural of filius (son) is filii. Apparently someone thought virus should have a plural ending in -ii because they saw the plural of filius and other second declension nouns ending in -ius and thought that all nouns ending in -us ended in -ii.
The confusion doesn't end there though. There is no example of the word virus being pluralized in any classical works. This wouldn't be a problem except that virus is an irregular noun. It's a neuter noun that is declined like a masculine second declension noun (except the accusative case which is also virus). In Latin (and Greek as well) neuter nouns have plurals that end in -a. Do not pass go. Do not collect $200. This is one of the most reliable rules in Latin (and in Latin most rules have very few exceptions in the first place). As such viri can't be the plural of virus either.
Then there are some people who upon hearing that virus is neuter mistake it for a third declension neuter noun and say that the plural of virus should be virora just as the plural of corpus is corpora. However, this cannot be the case since virus is known to have the genitive singular form viri and if it were a third declension noun it would have the form viroris.
Then there are other people who say that virus is a fourth declension noun but this doesn't make much sense since the genitive form doesn't match what would be expected for a fourth declension noun and as for as I know all fourth declension neuter nouns end in -u and not -us.
My best guess is that the plural of virus would be virus since this follows the pattern of other second declension neuter nouns with gender confusion issues. However, it's probably best to avoid all of this confusion and just pluralize it as viruses.
And now you know. And knowing is half the battle.

by NonSequor (230139)