In 2002, Gary McKinnon was arrested by the UK's national high-tech crime unit, after being accused of hacking into Nasa and the US military computer networks.
He says he spent two years looking for photographic evidence of alien spacecraft and advanced power technology.
America now wants to put him on trial, and if tried there he could face 60 years behind bars.
Banned from using the internet, Gary spoke to Click presenter Spencer Kelly to tell his side of the story, ahead of his extradition hearing on Wednesday, 10 May. You can read what he had to say here.
Spencer Kelly: Here's your list of charges: you hacked into the Army, the Navy, the Air Force, the Department of Defense, and Nasa, amongst other things. Why?
Gary McKinnon: I was in search of suppressed technology, laughingly referred to as UFO technology. I think it's the biggest kept secret in the world because of its comic value, but it's a very important thing.
Old-age pensioners can't pay their fuel bills, countries are invaded to award oil contracts to the West, and meanwhile secretive parts of the secret government are sitting on suppressed technology for free energy.
SK: How did you go about trying to find the stuff you were looking for in Nasa, in the Department of Defense?
GM: Unlike the press would have you believe, it wasn't very clever. I searched for blank passwords, I wrote a tiny Perl script that tied together other people's programs that search for blank passwords, so you could scan 65,000 machines in just over eight minutes.
SK: So you're saying that you found computers which had a high-ranking status, administrator status, which hadn't had their passwords set - they were still set to default?
GM: Yes, precisely.
SK: Were you the only hacker to make it past the slightly lower-than-expected lines of defence?
GM: Yes, exactly, there were no lines of defence. There was a permanent tenancy of foreign hackers. You could run a command when you were on the machine that showed connections from all over the world, check the IP address to see if it was another military base or whatever, and it wasn't.
The General Accounting Office in America has again published another damning report saying that federal security is very, very poor.
SK: Over what kind of period were you hacking into these computers? Was it a one-time only, or for the course of a week?
GM: Oh no, it was a couple of years.
A bird or a plane?... Gary was not able to get a picture of what he saw
SK: And you went unnoticed for a couple of years?
GM: Oh yes. I used to be careful about the hours.
SK: So you would log on in the middle of the night, say?
GM: Yes, I'd always be juggling different time zones. Doing it at night time there's hopefully not many people around. But there was one occasion when a network engineer saw me and actually questioned me and we actually talked to each other via WordPad, which was very, very strange.
SK: So what did he say? And what did you say?
GM: He said "What are you doing?" which was a bit shocking. I told him I was from Military Computer Security, which he fully believed.
SK: Did you find what you were looking for?
SK: Tell us about it.
GM: There was a group called the Disclosure Project. They published a book which had 400 expert witnesses ranging from civilian air traffic controllers, through military radar operators, right up to the chaps who were responsible for whether or not to launch nuclear missiles.
They are some very credible, relied upon people, all saying yes, there is UFO technology, there's anti-gravity, there's free energy, and it's extra-terrestrial in origin, and we've captured spacecraft and reverse-engineered it.
SK: What did you find inside Nasa?
GM: One of these people was a Nasa photographic expert, and she said that in building eight of Johnson Space Centre they regularly airbrushed out images of UFOs from the high-resolution satellite imaging. What she said was there was there: there were folders called "filtered" and "unfiltered", "processed" and "raw", something like that.
I got one picture out of the folder, and bearing in mind this is a 56k dial-up, so a very slow internet connection, in dial-up days, using the remote control programme I turned the colour down to 4bit colour and the screen resolution really, really low, and even then the picture was still juddering as it came onto the screen.
But what came on to the screen was amazing. It was a culmination of all my efforts. It was a picture of something that definitely wasn't man-made.
It was above the Earth's hemisphere. It kind of looked like a satellite. It was cigar-shaped and had geodesic domes above, below, to the left, the right and both ends of it, and although it was a low-resolution picture it was very close up.
This thing was hanging in space, the earth's hemisphere visible below it, and no rivets, no seams, none of the stuff associated with normal man-made manufacturing.
SK: Is it possible this is an artist's impression?
GM: I don't know... For me, it was more than a coincidence. This woman has said: "This is what happens, in this building, in this space centre". I went into that building, that space centre, and saw exactly that.
SK: Do you have a copy of this? It came down to your machine.
GM: No, the graphical remote viewer works frame by frame. It's a Java application, so there's nothing to save on your hard drive, or at least if it is, only one frame at a time.
SK: So did you get the one frame?
SK: What happened?
GM: Once I was cut off, my picture just disappeared.
SK: You were actually cut off the time you were downloading the picture?
GM: Yes, I saw the guy's hand move across.
SK: You acknowledge that what you did was against the law, it was wrong, don't you?
GM: Unauthorised access is against the law and it is wrong.
SK: What do you think is a suitable punishment for someone who did what you did?
GM: Firstly, because of what I was looking for, I think I was morally correct. Even though I regret it now, I think the free energy technology should be publicly available.
I want to be tried in my own country, under the Computer Misuse Act, and I want evidence brought forward, or at least want the Americans to have to provide evidence in order to extradite me, because I know there is no evidence of damage.
Nasa told Click that it does not discuss computer security issues or legal matters. It denied it would ever manipulate images in order to deceive and said it had a policy of open and full disclosure, adding it had no direct evidence of extra-terrestrial life.