Whether virus has a morphologically marked plural in latin is debatable. The discussion you link to claims that "virus" is a 4th declension noun, but all dictionaries I've checked (including Oxford!) says it's a 2nd declension noun. Anyway, "virus" is a neuter, not masculine noun, which means that the latin plural (if it really is 2nd declension) is not "viri" ("virii" does not make sense to me; is it an anglicism?), but "vira", which btw is well established as an alternative to "virus", at least in Denmark.
(The answer is of course: 4. A smartphone with a head-or-tails app.)
The most exciting phrase to hear in science, the one that heralds new discoveries, is not "Eureka!" (I found it!) but "That's funny ..." -- Isaac Asimov