A Mobile Ad hoc NETwork (MANET) is characterized by mobile nodes, multihop wireless connectivity, Non infrastructural environment and dynamic topology. In Ad Hoc network routing is the reactive on-demand philosophy where routes are established only when required. Stable routing, security and power efficiency are the major concerns in this field. The ad hoc environment is accessible to both legitimate network users and malicious attackers. This paper checks one of the common attacks on MANET as Intrusion detection and tries solving the situation.