Abstract: Wormhole attacks, in which colluding attackers with out-of-band communication links record packets (or bits) at one location and replay at another, cause far away nodes to consider themselves as neighbours to one another. Under this attack, two faraway malicious nodes can collude together using either wired link or directional antenna, to give an impression that they are only one hop away. We presents NEVO, in which nodes passively monitor (overhear) the forwarding of broadcast type packets by their neighbours and use the send and overhear times of trans- missions of these packets, to mitigate these wormhole attacks. NEVO does not require synchronized clocks, special hardware support, or any special capability.