Pasithea

Actually bogging down a system shouldn't be a huge problem in this scenario IMHO. Their environment would be a computer running a liniar OS with only limited processor cycles and ram and such, but it would likely take billions of iterations before Generation 0 stopped merely cloning itself and began to generate a mutant strain or two that were superior to it. By that time Generation 0 could be spread across billions of computers. Some computers would become infected with mutants that reproduce heedlessly until they consume their host computer(s) natural resources and crash the whole thing hence killing off their strain, successful mutations would have to try to be lean enough to reproduce prodigiously, but not overwhelm it's host system so that it could survive and spread to other computers, and replace the other old gen 0 viruses.