A (DDoS) distributed denial of service attack is one in which a multitude of compromised systems attack a single target, thereby causing denial of service for users of the targeted system. The flood of incoming messages to the target system essentially forces it to shut down, thereby denying service to the system to legitimate users.
In a hard DDoS attack, the assailant begins by exploiting a vulnerability in one computer system & making it the DDoS master. The attack master, also known as botmaster, identifies and infects other vulnerable systems with malware programs or files. Eventually, the assailant instructs the controlled machines to launch an attack against a specified target.
Type of DDoS Attacks:
There are two types of DDoS attacks-
1- A network centric attack which overloads a service by using up bandwidth and an application layer attack which overloads a service or database with application calls. The inundation of packets to the target causes a denial of service. The media tends to focus on the target of a DDoS attack as the victim, in reality there are many victims in a DDoS attack, the final target and as well the systems controlled by the intruder.
Although the owners of co opted computers are typically unaware that their computers have been compromised, they are nevertheless likely to suffer a degradation of service and not work well.
A computer under the control of an intruder is simply known as a zombie or bot. A group of co opted computers is known as a zombie army. But a funny things to know Kaspersky Labs and Symantec have identified botnets not spam, worms or viruses as the biggest threat to Internet security.