The NSA has patented (US patent 6,947,978) a method for locating Internet users based on their IP address by using the latency of connections with a network topology map. The highly secretive US Government agency cites geographically targeted advertising, disabling use of a password from a computer located outside of a specified area and signals intelligence as possible applications.
Depending on the accuracy, the technology might also be useful for tracing the origin of emergency phone calls over VOIP connections.