Protection Against DoS and DDoS Attacks
Definitions about DOS/DDOS attacks

What is a Denial of Service (DoS) attack?
A Denial of Service attack is designed to render a computer or network incapable of providing normal services. Common DoS attacks 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, and the computer can no longer process legitimate user requests.

What is a Distributed Denial of Service (DDoS) attack?
A Distributed Denial of Service attack uses many computers to launch a coordinated DoS attack against one or more targets. Using client/server technology, the perpetrator is able to multiply the effectiveness of the Denial of Service significantly by harnessing the resources of multiple unwitting accomplice computers which 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 computers anywhere on the internet. The agents, when they receive the command, initiate the attack. Using client/server technology, the master program can initiate hundreds or even thousands of agent programs within seconds.

How is a DDoS Attack executed against a website?
A website DDoS is executed by flooding one or more of the site's web servers with so many requests that it becomes unavailable for normal use. If an innocent user makes normal page requests during a DDoS attack, the requests may fail completely, or the pages may download so slowly as to make the website unusable.