Computer worm
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A computer worm is a self-replicating computer program, similar to a computer virus. A virus attaches itself to, and becomes part of, another executable program; however, a worm is self-contained and does not need to be part of another program to propagate itself. They are often designed to exploit the file transmission capabilities found on many computers.
The name 'worm' was taken from The Shockwave Rider, a 1970s science fiction novel by John Brunner. Researchers writing an early paper on experiments in distributed computing noted the similarities between their software and the program described by Brunner and adopted the name.
The first implementation of a worm was by two researchers at Xerox PARC in 1978. [1] (http://www.parc.xerox.com/about/history/default.html)
The first worm to attract wide attention, the Morris worm, was written by Robert Tappan Morris, Jr., who at the time was a graduate student at Cornell University. It was released on November 2, 1988, and quickly infected a great many computers on the Internet at the time. It propagated through a number of bugs in BSD Unix and its derivatives. Morris himself was convicted under the US Computer Crime and Abuse Act and received three years' probation, community service and a fine in excess of $10,000.
In addition to replication, a worm may be designed to do any number of things, such as delete files on a host system or send documents via email. More recent worms may be multi-headed and carry other executables as a payload. However, even in the absence of such a payload, a worm can wreak havoc just with the network traffic generated by its reproduction. Mydoom, for example, caused a noticeable worldwide Internet slowdown at the peak of its spread.
A common payload is for a worm to install a backdoor in the infected computer, as was done by Sobig and Mydoom. These zombie computers are used by spam senders for sending junk email or to cloak their website's address.[2] (http://seattletimes.nwsource.com/html/businesstechnology/2001859752_spamdoubles18.html) Spammers are thought to pay for the creation of such worms [3] (http://www.wired.com/news/business/0,1367,60747,00.html) [4] (http://www.channelnewsasia.com/stories/afp_world/view/68810/1/.html), and worm writers have been caught selling lists of IP addresses of infected machines.[5] (http://www.heise.de/english/newsticker/news/44879) Others try to blackmail companies with threatened DDOS attacks.[6] (http://news.bbc.co.uk/1/hi/technology/3513849.stm) The backdoors can also be exploited by other worms, such as Doomjuice, which spreads using the backdoor opened by Mydoom.
Whether worms can be useful is a common theoretical question in computer science and artificial intelligence. The Nachi family of worms, for example, tried to download then install patches from Microsoft's website to fix various vulnerabilities in the host system (the same vulnerabilities that they exploited). This eventually made the systems affected more secure, but generated considerable network traffic — often more than the worms they were protecting against — rebooted the machine in the course of patching it, and, maybe most importantly, did its work without the explicit consent of the computer's owner or user. As such, most security experts deprecate worms, whatever their payload.
External links
- The Wildlist (http://www.wildlist.org) List of viruses and worms 'in the wild' (i.e. regularly encountered by anti-virus companies)
- Worm parasites (http://www.2-spyware.com/worms-removal) Listed worm descriptions and removal tools.de:Computerwurm
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Computer worms evolved from viruses.