The system sometimes puts a completely unrelated sentence between those that relate to the skill, this is the algorythm and we can't do anything about it.
But with this example, it's actually more of a linguistic joke ;)
I get it And a wirus is like an animal or person, where the genitive and the accusative are the same.
Actually, a biological virus is not a living organism, so it's inanimate. However, the computer term "wirus", like other terms connected to computers and smartphones (mail, sms, facebook...) are treated as animate.
Ok, that was my theory... I checked and it turns out that in the case of biological viruses both forms are acceptable. Would be nice, if some natives commented what form they'd use.
I can imagine hearing "wirus" in the computer sentence, but generally I'd use "wirusa" with both.
Also, I don't expect most of the society to know that biological viruses aren't living organisms ;)