It has been discovered that stealth aircraft disrupts the signals between cell phone stations. Monitoring this disruption with special computer software would allow the flight of stealth aircraft to be tracked accurately. It is believed that the Serbs used a crude version of this technique in 1999 to shoot down a U.S. F-117 stealth bomber. With the right analysis software monitoring a cell phone network, stealth aircraft would no longer be stealthy. Since most nations now have cell phone networks, the survival of the stealth concept is in doubt.