  Mobile ad hoc networks (MANETs) are dynamic wireless networks without any
infrastructure. These networks are weak against many types of attacks. One of
these attacks is the black hole. In this attack, a malicious node advertises
itself as having freshest or shortest path to specific node to absorb packets
to itself. The effect of black hole attack on ad hoc network using AODV as a
routing protocol will be examined in this research. Furthermore, we investigate
solution for increasing security in these networks. Simulation results using
OPNET simulator depict that packet delivery ratio in the presence of malicious
nodes, reduces notably.
