Often when alleged UFO sightings in the United States and in various countries throughout the world occur the government will try and hide the incident reguardless if it is real or not, with a false report. They also prevent media coverage of Alien sightings.
Why do they do this?Edit
When alien sightings and alleged abductions arise. The news of aliens can cause panic and disruption within local communities and the wider world and could easy result in a state of emergency and mass culture and life changes. Reguardless of aliens are real are not. If the government tend to coverage up alien footage it could only suggest to us that they are real.
One famous coverup of alleged UFO evidence was the The Phoenix lights incident where large flashing lights were seen above the city of phoenix, in Arizona. The result was causing panic and problems, so the government allegedly claimed that the lights were not UFO's, but army jets. It is not quite sure whether this was true or not, but this  report speaks for itself.