US computer researchers have revealed a new danger to wireless network security. In a so-called ‘wormhole attack’ an intruder would intercept wireless data packets traveling across one part of a network and quickly re-insert them at another physical point on the network. ‘Ad-hoc’ wireless computer networks could be severely disrupted using the technique. These operate by passing communications from one node to the next until they reach their destination, rather than being controlled by a central server. Even if the network traffic were encrypted, an attacker would be able to control the data flow across the network. Wireless authentication systems could be duped. By relaying the authentication communication using concealed transceivers, an attacker could, for example, trick a door security system into opening. The researchers propose defending networks against the attack by attaching identifying tags, such as GPS information or a timestamp, to each packet. These tags let each node on the network determine where a packet has come from.