McKinnon's biggest fear, however, is that the US feels that it can hold people in Guantanamo Bay who aren't even accused of attacking the US. 

"I won't stand a chance in hell if I get extradited, because I will probably come under military order number one," he said.

"This means a secret military tribunal with a military lawyer, no rights of appeal, no rights of public comment and no press. It'll be Gary goes down a black hole and you don't see him again."

According to McKinnon, the top military brass claim that "it's where he's been and what he's seen" that poses the threat.

McKinnon has always asserted that he was hacking to discover the truth about UFOs and, while he's a free man, he is happy to discuss his findings.

"I was looking for suppressed technology and UFOs," he said. "I'd read a book by Stephen Greer called Disclosure that has expert testimonies ranging from civilian air traffic controllers and military radar operators, right up to the guys who are in charge of whether or not to launch nuclear missiles."

McKinnon claims that he found secret files on the Johnson Space Center's systems, including unprocessed and unfiltered photos in a proprietary Nasa image format. 

He describes a cigar-shaped object surrounded by domes, which looked like it was made from a single piece of metal without any seams.