Multihop wireless networks gain higher performance by using network coding. However, using network coding also introduces new attacks such as the well-studied pollution attacks and less-studied entropy attacks. Unlike in pollution attacks where an attacker injects polluted packets (i.e., packets that are not linear combinations of the packets sent by the source), in entropy attacks an attacker creates noninnovative packets (i.e., packets that contain information already known by the system). In both cases the result is a severe degradation of the system performance. In this paper, we identify two variants of entropy attacks (local and global ) and show that while they share some characteristics with pollution attacks and selective forwarding, none of the techniques proposed to defend against such attacks are applicable to entropy attacks because the packets look legitimate and the packet forwarding is stealthy in nature. We propose and evaluate several defenses that vary in detection capabilities and overhead.