A security attack is an action that compromises the security of information. Different security mechanisms have been developed to detect or prevent security attacks. There are different types of security attacks; interruption, interception, modification, and fabrication. Interruption occurs when somebody blocks the flow of information. In interception an attacker listens to the messages. In modification the message from the source is modified before reaching the destination. In fabrication an unauthentic party inserts spurious messages.