• Botnets. The term botnet (see Figure 1.7) can be used to refer to any group of bots,
or software robots, such as IRC bots, but this word is generally used to refer to a
collection of compromised computers (called zombies) running software, usually
installed via worms, Trojan horses, or backdoors, under a common command-andcontrol
infrastructure. The majority of these computers are running Microsoft
Windows operating systems, but other operating systems can be affected.