It is known that 802.11 is not resilient to selfish behavior and denial of service (DoS) attacks targeting the MAC layer. In this study, we assess the performance of the CSMA/CA scheme and investigate its efficiency with regard to security and information assurance in mobile ad hoc wireless networks. We investigate several variants of selfish node behaviors that abuse the random choice of Contention Window in the 802.11 DCF MAC protocol. We show that selfish behavior in the MAC layer can have devastating side effects on the performance of wireless networks, similar to the effect of DoS attacks. Our main contributions are the prevention and detection of backoff manipulation in an ad hoc network. First, we propose an algorithm to prevent backoff manipulation in a communication link between a sender and a receiver when at least one of the nodes behaves honestly. Secondly we introduce algorithms for detection of backoff manipulation by a pair of colluding nodes.