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 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.

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