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The term Denial of Service (DoS) refers to a form of attacking computer systems over a network. DoS is normally a malicious attempt to render a networked system unusable (though often without permanently damaging it).

Denial of service relies on methods that exploit the weaknesses of network technology. For example, one common form of DoS is Ping of Death. Ping of Death attacks work by generating and sending certain kinds of network messages that are technically unsupported but known to cause problems for systems that receive them. Denial of service attacks like Ping of Death may crash or "hang" computers. Other DoS attacks may simply fill or "flood" a network with useless data traffic, rendering systems incapable of acting on bona fide requests.

DoS attacks are most common against Web sites that provide controversial information or services. The commerical cost of such attacks can be very large. DoS may also occur unintentionally when developing or upgrading network systems.
Also Known As: Denial of Service, Distributed Denial of Service (DDoS)

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Posted by saqlain231

Action(s) which prevent any part of an AIS from functioning in accordance with its intended purpose.

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Posted by HamidAliKhan

A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer resource unavailable to its intended users. Although the means to carry out, motives for, and targets of a DoS attack may vary, it generally consists of the concerted, malevolent efforts of a person or persons to prevent an Internet site or service from functioning efficiently or at all, temporarily or indefinitely. Perpetrators of DoS attacks typically target sites or services hosted on high-profile web servers such as banks, credit card payment gateways, and even DNS root servers.

One common method of attack involves saturating the target (victim) machine with external communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consume its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.

Denial-of-service attacks are considered violations of the IAB's Internet Proper Use Policy. They also commonly constitute violations of the laws of individual nations

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Posted by sagitraz

http://compnetworking.about.com/od/networksecurityprivacy/g/denialofservice.htm

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Posted by eric