Denial of Service (DoS)

A denial of service (DoS) attack prevents system availability by breaking or overloading some key system component. For example, DoS can be achieved through overloading a server or a firewall with excessive volumes of spurious network traffic.

When a DoS attack is launched from multiple simultaneous hosts, the resulting exploit is called distributed denial of service (DDoS).

References:

http://www.us-cert.gov/cas/tips/ST04-015.html

http://www.denialinfo.com/