Mobile ad-hoc networks (MANETs) have attracted significant research attention recently because of the fast growth of laptops, personal digital assistant, and 802.11/Wi-Fi wireless networking. However, the flexible deployment nature and the lack of fixed infrastructure make MANETs suffer from a variety of security attacks. In this paper, we show how an adversary can utilize a colluding injected attack (CIA) in MANET by injecting malicious nodes in the network, while hiding their identities from other legitimate nodes. These injected nodes will work together (colluding) to create a collision at an arbitrary node, thus preventing it from receiving or relaying any packet. Because of this collision, a legitimate node could be reported as malicious nodes by monitoring nodes in the neighborhood. In this work, we propose a monitoring verification scheme to mitigate the effect of the CIA attack. Our proposed scheme is able to accurately detect malicious nodes in the network compared with previous detection schemes. Through simulations, we show that our proposed scheme outperforms previous detection schemes in terms of true/false detection of any malicious behavior in the network caused by the CIA attack. Copyright © 2013 John Wiley & Sons, Ltd.