In this paper, the authors consider a scenario where nodes in a MANET disseminate data chunks using rate-less codes. Any node in MANET is able to successfully decode any chunk by collecting enough coded blocks from several other nodes without any coordination. Here the problem is to identify malicious nodes that launch a pollution attack using sieve a decentralized, accurate and robust technique that exploits rate-less codes which detect chunk integrity. Source nodes transmit data using Luby transform codes (a class of rate-fewer codes) and any legitimate node in a WMN executes a randomized and fully distributed detection mechanism to detect its malicious neighbors and it is isolated subsequently.