Along with the revolution in communication and information exchange, Internet has also provided greater opportunity for disruption and sabotage of data that was previously considered secure. As malicious intrusions into computer systems have become a growing problem, the need for accurate detecting these intrusions is raised. Intrusion detection becomes an increasingly important technology that monitors network traffic and identifies unauthorized use, misuse and abuse of computer systems. Since normal and abnormal behaviors in computer systems are hard to predict as the boundaries can not be...