LANGLEY, Va., Dec. 29 (UPI) -- The CIA noted via Twitter Monday that it was responsible for at least half of UFO sightings in the 1950s and 60s.

"Reports of unusual activity in the skies in the '50s? It was us," the agency tweeted.


The document the tweet links to is a previously confidential report on the testing of the U-2 spy plane at altitudes of over 60,000 feet. It says half or more of supposed UFO sightings were actually times when they were flying the plane at high altitudes, which people didn't realize was possible at the time.

Though they realized people were spotting the plane by cross-referencing the sightings with when and where the plane was flying, the agency couldn't inform the public of that knowledge. The agency says the document explaining that scenario was the most widely read document released this year from their database.

The U-2 is now flown by the United States Air Force, and 104 have been built in total. One was shot down by the Soviet Union in May of 1960 at 70,500 feet during the first attempt to cross the Soviet Union by going from Pakistan's air space to Norway's.