However wrong it may be, lots of people have pluralized virus as virii. I'd understand viri, but what misconception could lead one to write virii?
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I suspect the confusion arises out of the fact that very few people now have any kind of understanding of Latin. Many words get turned into faux-Latin plurals, even when the word itself is not Latin in origin, or when the plural form is completely incorrect (octopi, platypi, penii). It seems to come up most often when the plural form of the word has an -ses construction. It feels uncomfortable to say, so people (often jokingly, in my experience, but occasionally earnestly) try to give it a faux-Latin plural.
On the Italian Wikipedia page for Virus, it seems that there are different plurals used in different contexts.
I can't quote it because it's italian and almost no-one will understand so I'll try to translate the important parts: