A particularly severe attack on routing protocols in ad hoc networks is the so-called wormhole attack in which two or more colluding attacking nodes record packets at one location, and tunnel them to another location for a replay at that remote location. When this attack targets specifically routing control packets, the nodes that are close to the attackers are in effect shielded from finding any alternative routes to the remote location with more than one or two hops, and thus all the routes will be directed to the wormhole established by the attackers. In optimized link state routing protocol (OLSR), if a wormhole attack is launched during the propagation of link state packets, the wrong link information will propagate throughout the network, leading to routing disruption. In this paper, we devise an efficient method to detect wormhole attacks in the OLSR protocol. This method tries to ascertain the effective presence of neighbors by employing an efficient neighborhood detection algorithm. Our method has several advantages since it does not require any time synchronization or location information and shows high detection rate under various scenarios.