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-positioning 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.