Hearsay, the lot of it.

Not a single solid shred of evidence has ever been shown, put in a museum or made available for serious objective study. There is no evidence anyone can bring forth to support the claim UFOs have anything to do with extraterrestrials or that an alien being has ever set foot upon this planet.

Taken from Amos's link:

"Evidence is everywhere – from worldwide religious and mythological accounts commonly describing ancient encounters with advanced beings, anomalous archaeological sites and artifacts indicating past use of superior technology, over a century's worth of eyewitness sightings of UFOs, hundreds of physical trace samples recovered from UFO landing sites, government documents and whistleblowers acknowledging the existence of extraterrestrials, and thousands of abduction cases that include multiple witnesses, memories recalled without hypnosis, and undisputable physical and medical evidence confirming these accounts."

This statement is a pile of utter rubbish - show me now this"undisputable physical and medical evidence . . . Tell me where I can see it - not a photo, but the real thing.