Networks are protected using many firewalls and encryption software's. But many of them are not sufficient and effective. Therefore an intrusion detection system (IDS) is required that monitors the network, detects misbehavior or anomalies and notifies other nodes in the network to avoid or punish the misbehaving nodes. Numerous schemes have been proposed for intrusion detection and response systems, for ad hoc networks. The ultimate goal of the security solutions for wireless networks is to provide security services, such as authentication, confidentiality, integrity, anonymity, and availability, to mobile users. In this paper, we examine the vulnerabilities of wireless networks and argue that we must include intrusion detection in the security architecture for mobile computing environment. We propose a mIDS (mobile intrusion detection system) suitable for multi-hop ad-hoc wireless networks, which detects nodes misbehavior, anomalies in packet forwarding, such as intermediate nodes dropping or delaying packets. mIDS does rely on overhearing packet transmissions of neighboring nodes. Simple rules are designed to identify the misbehavior nodes. Theproess of identyfing the misbehavior node is carried out by a special node called a monitor node. Periodically monitor node is identified in the network.