A Mobile Ad-hoc NETwork (MANET) is a collection of mobile nodes that can has no fixed or predetermined topology, with mobile nodes and dynamic membership changes. A self-organizing network is a network that can automatically extend, change, configure and optimize its topology, coverage, capacity, cell size, and channel allocation, based on changes in location, traffic pattern, interference, and the situation or environment. MANETs due to complete autonomy of the member nodes and lack of any centralized infrastructure are particularly vulnerable to different types of attacks and security threats. Packet drop attack is one of them. In this paper mechanism has been proposed to detect and defend against packet drop attacks.