DOS attack is a term which stands for denial of service attack. Denial of service is a type of computer attack instigated most often by hackers or terrorists who wish to shut down or disrupt Internet services. Denial of service attacks are perpetrated many ways, but the three most common are bandwidth consumption, resource consumption, and network connectivity.

Bandwidth Consumption DOS attacks

Bandwidth consumption DOS attacks used to be done by groups of hackers who flood the targeted website with useless data packets which stops legitimate users from accessing the unfortunate website. This method is called a flood DOS attack. A flood DOS attack used to require a significant degree of coordination and communication between hackers. In 1999 a new type of flood DOS attack was instigated called a zombie flood DOS attack. A zombie flood DOS attack is when a single person infects several even hundreds of unsuspecting computers and controls them remotely to attack a single target. The unsuspecting computers act as zombies unknowingly attacking the perpetrator's intended target.

Resource Consumption DOS Attacks

Resource consumption DOS attacks are when network resources are overburdened and cause the rest of the network to slow down. A popular target for resource consumption are pop3 mail servers. A computer which is connected to the network but is unknowingly infected could start sending out a thousands even millions of emails. The network recognizes the computer and email requests as legitimate and there for tries to process them. In the process of trying to send out millions of emails the network get bogged down and grabs resources from other places so that other network uses lose their connections.

Network Connectivity DOS attacks

In this type of denial of service the attacker attempts to force the server not to communicate on the network and hence denies a service. This is different from bandwidth consumption DOS attacks in that the bandwidth remains open, just that the attacker has denied access to it.

What to Do About DOS Attack

Antivirus software can have limited effects on DOS Attacks, mostly by preventing resource consumption DOS attacks if the software is properly updated. Once an attack begins both firewalls and antivirus software becomes useless. The only real solution is application front end hardware, which can recognize a DOS attack as it happens. By recognizing the attack as it is happening the application front end hardware can divert resources to legitimate users and deny the attackers access.

The current leader in application front end hardware is Radware.