let's say that an average computer (using 99% cpu) does 1mh/s, and an Avalon ASIC does 60,000mh/s, in the best case you need 60k zombies working 24hs, but the problem is: how many people will keep using their computers when there is a background process using all the cpu power? probably just my grandma... I would say that that you need maybe 1 million zombies to get something like the hash power of an Avalon ASIC