Are UFOs a threat to national security ?

On the afternoon of Nov. 7, 2006, pilots and airport employees at O'Hare International Airport in Chicago saw a disc-like object hovering over the tarmac for several minutes. Because nothing was tracked on radar, the Federal Aviation Administration did not investigate. Yet radar is not a reliable detector of all aircraft. Stealth planes are designed to be invisible to radar, and many radar systems filter out signals not matching the normal characteristics of aircraft. Did it really make sense to entirely ignore the observations of several witnesses? A healthy skepticism about extraterrestrial space travelers leads people to disregard U.F.O. sightings without a moment's thought. But in the United States, this translates into overdependence on radar data and indifference to all kinds of unidentified aircraft — a weakness that could be exploited by terrorists or anyone seeking to engage in espionage against the United States.The American government has not investigated U.F.O. sightings since 1969, when the Air Force ended Project Blue Book, an effort to scientifically analyze all sightings to see if any posed a threat to national security. Britain and France, in contrast, continue to investigate U.F.O. sightings, because of concerns that some sightings might be attributable to foreign military aircraft breaching their airspace, or to foreign space-based systems of interest to the intelligence community. - mystery