UFOs =/= Aliens
Not that there is any good explanation otherwise for what all these people have seen or what we apparently recorded, but Occam's Razor and all that.
I'm with @RHmostly, though I don't think it is probably another government; there would be more of a paper trail and/or more people out there that have slipped up something.
I'd put my money one some private company and/or individuals developed something crazy and just haven't been found out yet. They say on 60 minutes that it's been "daily for a few years now"? Which would suggest to me it's not all that old necessarily. That's where my mind is at currently.
I hope maybe we'll find out more in a month when that big D.O.D. report is being released to the public.