Manet routing protocols are designed based on the assumption that all nodes cooperate without maliciously disrupting the operation of the routing protocol. aodv is a reactive manet routing protocol that is vulnerable to a dramatic collapse of network performance in the presence of black hole attack. the paper introduces a new concept of self-protocol trustiness (spt) in which detecting a malicious intruder is accomplished by complying with the normal protocol behavior and lures the malicious node to give an implicit avowal of its malicious behavior. we present a blackhole resisting mechanism (brm) to resist such attacks that can be incorporated into any reactive routing protocol. it does not require expensive cryptography or authentication mechanisms, but relies on locally applied timers and thresholds to classify nodes as malicious. no modifications to the packet formats are needed, so the overhead is a small amount of calculation at nodes, and no extra communication. using ns2 simulation, we compare the performance of networks using aodv under black hole attacks with and without our mechanism to saodv, showing that it significantly reduces the effect of a blackhole attack.