One of the methods of those using the Internet for illegal purposes is to grab control of your computer and use it to distribute spam and viruses anonymously. A computer taken over in this way is known to hackers as a zombie. A more sinister recent development has been the entry of organised crime groups, who harness networks of these zombies, called botnets (where bot is an abbreviation for robot). The aim in this case is not usually to send spam but to bring down a Web site through what’s called a distributed denial-of-service attack. The network of zombies is told to send a very large number of request signals to the site all at once, so denying access to legitimate users and possibly causing the Web server to collapse under the load. There have been reports that this type of attack has been used for blackmail, especially of gambling sites and financial institutions, and obvious risks exist of its being used for terrorism. The term botnet has been known in the hacker community at least since the middle 1990s, but has only recently started to appear in more general contexts.
This modus operandi is fuelling a growing crime wave against e-commerce in which these networks of bots, dubbed botnets, are increasingly being offered for hire by hacking groups.
New Scientist, 6 Nov. 2004
A more sinister use of botnets is sabotage, police say. A fear is growing that a botnet could be used to take down a major data network or prominent Web sites.
Birmingham Post, 13 Jul. 2004