A former British Ministry of Defence expert recently looked over four films claiming to show UFOs and gave his verdict.
Nick Pope was employed by the Ministry of Defence to investigate alien abduction and sightings as part of their now defunct UFO Project.
Over more than 20 years, he had to analyse hundreds of possible sightings and encounters to decide whether they had any merit or were a threat to Britain's "territorial integrity".
Now he has cast his expert eye over some of the most intriguing recent films to test their authenticity.
As part of his tour to promote the Hollywood film Battle:LA, which has been released on DVD, he examined filmed evidence of visitations from other worlds from London, Sao Paulo, Jerusalem and Moscow. The truth, as they say, is out there.
"A UFO over London gets everyone's attention.
"The slightly suspicious thing though, is it's in a part of London where it just so happens a large number of film companies and visual effects companies are based.
"Some of the people do look a little bit self-satisfied, so i suspect this is a CGI hoax and someone is showcasing their skills."
"What's fascinating about this.. is this idea of the UFO almost playing cat and mouse with observers, the way it ducks in and out of the cloud, as if it's playing games with the witnesses, just giving you a glimpse but not so much you can really tell what it is.
"Does that mean that there's an intelligence behind the UFO or is the intelligence really someone who made this on a computer?
"With all these videos, unless you can get access to the witnesses, unless you can ask the air force if something was tracked on radar, it's almost impossible to tell."
"This video taken in Jerusalem is actually one of a series of about three or four different videos and at first people took this as proof that it must be real - look, tourists all around the city have seen the same thing but from different angles.
"That raises the question, if somebody is actually making a fake film and is really trying to kid people, then it is little extra work to maybe make those extra videos.
"The very thing that people say is proof that it's real is actually proof that someone put a lot of thought into this, but at the end of the day, it's just another fake."
"This sort of UFO - this large triangular shape - is a shape that's been reported all around the world in the last 10 or 20 years.
"I think the problem with a video like that is you could say if something obviously that big really had been hovering over Red Square in daylight, there would be tens of thousands of witnesses, it would have be have tracked on radar and the air force would have scrambled jets and maybe fired on the thing.
"As far as I'm aware none of that ever happened.
"It's an interesting piece of footage but there are some question marks over it too."
A fisherman who claimed to be abducted and then rejected by aliens for being "too old and infirm" and two policemen who spotted a spaceship hovering over a road are among a list of close encounters revealed by Britain's very own X-file investigator.