Security of Information is one of the cornerstones of Information Society. As number of Network attacks have increased over the past few years, Intrusion Detection System (IDS) is increasingly becoming a critical component to protect the network. In recent years, many researchers are using data mining techniques for building IDS. One of the main challenges in the security management of large-scale high-speed networks is the detection of suspicious anomalies in network traffic patterns due to Distributed Denial of Service (DDoS) attacks or worm propagation.