DoS attack 
denial-of-service attack 
An assault on a computer network or a server that floods it with so many superfluous requests that service is either slowed or interrupted. Common types of DoS attacks include buffer overflow and smurf attacks. In a buffer overflow attack, the assailant overwhelms the target system with oversized data packets or with e-mail messages that have unusually large file names. In a smurf attack, the assailant sends an IP ping request to a server with instructions to broadcast the request to a number of hosts within the server's network. The return address on the request is falsely identified (spoofed) as the server targeted to receive the DoS attack. The result is that a flood of ping replies overwhelm the targeted server.