Normal viruses carry genes for the proteins that are needed to make more viruses. (newscientist.com)
This makes sense: By driving the proliferation of infected cells, viruses speed manufacture of more viruses, but excessive cellular proliferation is also a hallmark of cancer. (sciencedaily.com)
The level is cleared when all the viruses have been removed from the playing field and a new level is then approached where there are even more viruses than the previous one. (nintendolife.com)