What Is Denial Of Service?

A Denial of Service (DoS) attack renders computers and networks incapable of providing normal services. Common DoS attacks typically target the network bandwidth or server connectivity. Bandwidth attacks flood the network with such a high volume of traffic, that all available network resources are consumed and legitimate user requests cannot get through. Connectivity attacks flood a computer with such a high volume of connection requests, that all available operating system resources are consumed. Once that happens, the computer can no longer process legitimate user requests.

Denial of Service (DoS)

Distributed Denial of Service (DDoS)
What Is Distributed Denial Of Service?

A Distributed Denial of Service (DDoS) attack uses many computers to launch a coordinated DoS attack against one or more targets. Using client/server technology, the attacker is able to multiply the effectiveness of the Denial of Service significantly by harnessing the resources of a multitude of unsuspecting computers. These "accomplice" computers serve as attack platforms. Typically a DDoS master program is installed on one or more computers using a stolen account. The master program, at a designated time, then communicates to any number of "agent" programs, installed on a network (botnet) of computers around the internet. The agents or botnet computers, when they receive the command, initiate the attack on the single server where the harm is meant to occur. Using client/server technology, the master program can initiate hundreds or even thousands of agent programs within seconds, in turn overwhelming the unprotected target server with large numbers of requests.

What is a Botnet?

A botnet is a number of computers (zombies) connected to the internet that, although their owners are unaware of it, have been set up to transmit spam or virus attacks to other computers on the internet. These zombie computers in effect serve the wishes of a master spam originator and often target a single server or organization. Most compromised zombie computers are home-based with an internet connection. Today, network experts agree that botnets pose the biggest threat to the internet.

The computers that form a botnet can be programmed to redirect transmissions to a specific computer for a malicious purpose. A typical example would be an attempt to shut down a website by sending too much traffic to it. The motivation for a zombie master who creates a DDoS attack may be to blackmail, gain a competitive advantage, politically undermine, create an electronic protest or a whole host of other reasons. The zombie computer owners are usually unaware that their systems have been compromised and are part of an attack.

Diagram of a Distributed Denial of Service Network (DDoS Network)