Now-a-days, use of computer with internet becomes very popular technology but the use of this is most susceptible to severe attack. It is key challenge for the user to protect their personal information and resources from the attack. An intrusion detection system is the process for identifying attacks on network. Intrusion detection system is categorized into two types: Anomaly based and misuse based detection. The data mining techniques make feasible to observe the network to thwart it from the intruders such as k-means and PSO (Particle Swarm Optimization) etc.