An ad hoc network is the assortment of cooperative wireless nodes without existence of any access point or infrastructure. Many ad hoc network routing protocols have been proposed in the literature. However, none of them deal with the issues of security. The presence of malicious nodes in an ad hoc network deteriorates the network performance. A novel approach for enhanced intrusion detection system for malicious node is proposed here to protect against attacks in ad hoc on-demand distance vector routing protocol. The proposed approach employs a method for determining conditions under which malicious node should be monitored. Apart from identification of malicious node, it has been observed that this approach leads to less conservation and less communication breakage in ad hoc routing. The experimental results demonstrate that the proposed approach can effectively detect malicious nodes. This approach has been found beneficial for identifying malicious nodes in black hole attack, neighbour attack, sequence number attack and packet forwarding attack up to 700 nodes.