is designed just to cause an interruption to a system or network temporarily, denying access to legitimate users. This interruption in turn can cause loss of money and reputation by preventing customer access to online services. These attacks usually target specific services and attempt to overwhelm them by making numerous requests concurrently. If a system is not protected to react to a DoS attack, it can be easily brough down by running scripts that generate a very large number of requests. Some examples of Denial of Service (DoS) attacks are detailed below.