An attack on a computer system which results in the service being offered to a user or a number of users being severely degraded. Usually this degradation is so serious that the users are unable to interact effectively with the computer that is the subject of such an attack. An example of such an attack is one where a virus infects a computer and takes over the processor by executing a large number of high-priority programs which carry out some slow process such as reading a file. This would result in any user programs having their access to the processor severely curtailed. Another example is email flooding where a large volume of emails causes major problems for an email server. Other examples include SYN flooding, ping flooding, and black widow. It is also known as a degradation of service attack.