“Bot” is a shortened form of robot and is a name for programs that perform repetitive tasks. When used maliciously, bots make it possible for hackers to control thousands of “zombies” (PCs hijacked by hackers) as easily as they can control one. A botnet is a group of bot infected PCs that are all controlled by the same hacker. Botnets can be used to send spam, download and store illegal files, such as porn, or to make computers participate in attacks on other computers. A botnet can be used to flood a specific Web site with traffic, to the point where it is overwhelmed and cannot respond to normal traffic, effectively taking it offline (called a Denial of Service attack).