Distributed Denial of Service, DDOS attack
A Distributed Denial of Service or DDOS attack uses many machines to attack one system or network. One method to do this was to do a broadcast ping to an entire subnet and fake the sender of the ping making it look like the sender was the intended target (smurf attack). This would cause a flood of ping replies to the target.
Attackers may also use many compromised hosts to implement a distributed denial of service (DDOS) attack. The attacker may use a virus or worm to gain control of many computer systems on the internet. In doing this he is exploiting a vulnerability in the computer systems on the internet to gain control of them. The attacker may control thousands of computers. The attacker can then instruct the machines under their control to flood a specified target with many requests for information. The requests may be pings or requests for web pages. The intent is to overload the single target and render it unusable thus denying service from that target to any users.
The victims in this case include the target computer system, the compromised machines, and the users attempting to use the targeted computer system.