Compass, face and geographical routing, for ad hoc and wireless sensor networks, rely on nodes knowing their geographic location and locations of other nodes. For location-unaware nodes without self-positiong devices (e.g., GPS), Garcia-Alfaro et al. proposed location determination algorithms leveraging location reports from neighbors. The evil ring is an attack on the location determination algorithms of Garcia-Alfaro et al. When inquired, an attacker returns a fake location sitting on a circle centered at the victim?s location and with radius equal to the attacker-victim separation distance. The calculation of the distance between the victim and attacker is not affected. A location-unaware node correctly determines its location. The attack, however, misleads into getting and using wrong locations of neighbors. We introduce and analyze an evil ring attack detection algorithm. Location-unaware nodes crosscheck consistency of information collected from neighbors. Neighbors perpetrating the evil ring attack are uncovered. O(n) messages are sufficient to localize all location-unaware nodes, to detect all liars, and to construct valid neighbor tables. Simulation results demonstrate that our algorithm, named Cross Check, outperforms the Garcia-Alfaro et al. algorithm Majority-ThreeNeighborSignals. We compared the percentage of locationunaware nodes that successfully derive valid neighbor tables. Simulations were conducted under equivalent topology conditions, varying the percentage of evil ring attack perpetrators.