Botnets silently control your PC

A major form of cyber-crime today, not always well understood by computer users, is the "botnet." The word is geek-speak for "robot network." A botnet consists of a large number of computers — in one case, more than a million — that have been enslaved by a hacker and operate under his command. (He is called a "botherder" or "botmaster," and the infected computer is a "zombie.") These are then used for various illegal purposes, such as sending huge amounts of spam. The misbehavior goes on in the background so that you probably won't notice it.

The hacker plants malware, meaning software used for malevolent purposes, on your computer. He can do this by using viruses, worms, or Trojans. For example, he can fool you into clicking on an e-mail attachment that plants the program. Another is the "drive-by," in which an infected Web site does the same when you visit. Porn and gambling sites are notorious for this.

Your computer then automatically connects, under the control of the malware, to a central server somewhere. You don't know that it is doing this. Countless other computers, also compromised, do the same.