An ad hoc network is a collection of mobile nodes that dynamically form a temporary network. It operates without the use of existing infrastructure. As mobile ad hoc network applications are deployed, Routing is one of the central requirements. Due to non central control, security is the major issue in MANET. Existing AODV defines no special security mechanisms. So an impersonation attack can be easily done. This paper analyzes the performance of AODV routing protocol in the presence of malicious nodes using network simulator NS2.34 on Ubuntu 10.04. The metrics for evaluation has been considered as Packet Delivery Ratio, end to end delay ratio, throughput, data packets sent/received and control packets drop.