Wireless sensor networks (WSNs) are often deployed in harsh environments.Thus adversaries can capture some nodes,replicate them and deploy those replicas back into the strategic positions in the network to launch a variety of attacks.These are referred to as node replication attacks.Some methods of defending against node replication attacks have been proposed,yet they are not very suitable for the mobile wireless sensor networks.In this paper,we propose a new protocol to detect the replicas in mobile WSNs.In this protocol,polynomial-based pair-wise key pre-distribution scheme and Counting Bloom Filters are used to guarantee that the replicas can never lie about their real identifiers and collect the number of pair-wise keys established by each sensor node.Replicas are detected by looking at whether the number of pair-wise keys established by them exceeds the threshold.We also derive accurate closed form expression for the expected number of pair-wise keys established by each node,under commonly used random waypoint model.Analyses and simulations verify that the protocol accurately detects the replicas in the mobile WSNs and supports their removal. Wireless sensor networks (WSNs) are often deployed in harsh environments. Where are advasion can capture some nodes, replicate them and deploy those replicas back into the strategic positions in the network to launch a variety of attacks.These are referred to as node replication attacks. Some methods of defending against node replication attacks have been proposed, yet they are not very suitable for the mobile wireless sensor networks. This paper, we propose a new protocol to detect the replicas in mobile WSNs.In this protocol, polynomial-based pair -wise key pre-distribution scheme and Counting Bloom Filters are used to guarantee that the replicas can never lie about their real identifiers and collect the number of pair-wise keys established by each sensor node. Replicas are detected by looking at whether the number of pair-wise keys established by them exceeding the threshold. We also derive accurate closed form expression for the expected number of pair-wise keys established by each node, under commonly used random waypoint model. Analyses and simulations verify that the protocol accurately detects the replicas in the mobile WSNs and supports their removal.