My dad's a retired air traffic controller. But when he was first getting started in air traffic control, he was in the Air Force. One day he was sitting at the radar scope doing his thing, when an unidentified blip came on screen. No communication or warning whatsoever. But the weird part was that this object was moving across his screen at a rate indicating *incredible* airspeed, and making sharp angle course adjustments not even attainable by -todays- aircraft. And to top it off he had two pilots see it pass close to them and radio in asking him wtf it was. So, he called over his supervisor, a higher ranking officer.
According to him, his supervisor looked at the screen and all he said was "I don't see anything...Do you?" And a few minutes later a fighter wing was chasing after where the thing was headed.
Apparently there's been a good few stories like this among ATCs, but they never get reported because seeing UFOs like that isn't considered 'normal' behavior, and runs a high risk of losing one's job.
Anyway. I personally do believe in UFOs, because there's too many 'group encounters' -like entire towns seeing the same thing at the same time- for them to be fraudulent. However, I also believe that for every real UFO encounter there's got to be at least two that are BS. Some are real, but some are hoaxes.