On the Internet, a denial of service (DoS) attack is an incident in which a user or organization is deprived of the services of a resource they would normally expect to have. Typically, the loss of service is the inability of a particular network service, such as e-mail, to be available or the temporary loss of all network connectivity and services.

In the worst cases, for example, a Web site accessed by millions of people can occasionally be forced to temporarily cease operation. A denial of service attack can also destroy programming and files in a computer system. Although usually intentional and malicious, a denial of service attack can sometimes happen accidentally. A denial of service attack is a type of security breach to a computer system that does not usually result in the theft of information or other security loss. However, these attacks can cost the target person or company a great deal of time and money.

Attacks typically start with crude SYN Flood attacks. If that doesn’t scare targets, then attackers resort to more sophisticated attacks (SYN Floods, UDP Floods, NB-Gets, ICMP Ping Floods and UDP Fragment Attacks). The effect on unprotected sites can be devastating.

But firms in the insurance sector, payment companies and even ISPs are also at risk. Small businesses are also at risk because of the excess bandwidth charges arising as a result of DDoS attacks. The number, frequency and intensity of DDoS attacks is starting to "go through the roof". Whether the motive is extortion, personal vengeance or mischief anyone can be a target....

A DDoS (Distributed Denial of Service) attack a hacker usually uses a botnet, a network of enslaved computers placed under the hacker’s control. The botnet receives remote commands and executes them. In a successful DDoS attack, all the enslaved computers send huge amounts of requests to the targeted company’s DNS servers, flooding the DNS servers with data. All these requests look legitimate so the DNS security measures are useless.

Updated On: 13.05.12