Microsoft Does China
"Botnets are large numbers of infected PCs, known as zombies, under the control of botherders (the people who run the networks, botnets, of zombies). Zombies are created by hackers, who write computer viruses that get into your computer from an infected website or booby trapped file attachment to spam email.
Currently, on any given day a few percent of all the computers on the planet are zombiefied. These captive computers are organized into botnets of thousands, or millions, of PCs that do the bidding of their controllers. The most common use of botnets is transmitting spam, and secret programs that create more zombies, or steal information (government secrets, or your banking information.) Internet criminals spend most of their time seeking out poorly protected PCs connected to the Internet that can be turned into zombies. This can cost up to a dollar per zombie PC. The "owners" of these zombies then uses them to make money (sending spam, launching DDOS attacks, for the most part.) Some botnet owners rent their zombies out. There is no honor among thieves, either, with some Internet crooks seeking out botnets, and using their tools to try and take control. The good guys play this game as well, seeking out the botnets, and purifying the infected machines by finding and deleting the hidden software that makes a PC a zombie."