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.