In this paper ,we study the types of attacks in intrusion detection system in Mobile Ad Hoc network(MANET).Mobile Adhoc Networks are a relatively new and rapidly evolving area of interests. One such field concerns mobile adhoc networks (MANETs) in which mobile nodes organize themselves in a network without the help of any predefined infrastructure. Securing MANETs is an important part of deploying and utilizing them, since they are often used in critical applications where data and communications integrity in important. Many solution for intrusion detection in wireless environments have been developed but these solution may not always be sufficient, as ad-hoc networks have their own vulnerabilities that cannot be addressed by these solutions. In this paper traditional security algorithms coupled with intrusion detection mechanism. Here we using a quantitative method to detect intrusion in MANETS with mobile nodes. Our method is a behavioral anomaly based system, which makes it dynamic, scalable, configurable and robust. For simulating our mobile nodes use AODV (Adhoc on demand distance Vector)routing. It is observed that the malicious node detection rate is very good and false positive detection rate is slow.