A mobile ad-hoc network is a collection of mobile nodes connected together over a wireless medium without any fixed infrastructure. Unique characteristics of mobile ad-hoc networks such as open peer-to peer network architecture, shared wireless medium and highly dynamic topology, pose various challenges to the security design. Mobile ad-hoc networks lack central administration or control, making them very vulnerable to attacks or disruption by faulty nodes in the absence of any security mechanisms. Also, the wireless channel in a mobile ad-hoc network is accessible to both legitimate network users and malicious attackers. So, the task of finding good solutions for these challenges plays a critical role in achieving the eventual success of mobile ad-hoc networks. Here we propose an “unobtrusive monitoring” technique, that uses readily available information from different layers of the protocol stack to detect “malicious packet-dropping”, where a faulty node silently drops packets destined for some other node. A key source of information for this technique is the messages used by the special ad-hoc routing protocols. This technique can be deployed on any single node in the network without relying on the cooperation of other nodes, easing its deployment.