The former National High Tech Crime Unit arrested McKinnon in 2002,
three years after he began looking for evidence of extra-terrestrial beings and technologies on US computers.
McKinnon was obsessed with finding evidence that the US government
was hiding alien technology that would provide free energy.
Had he found it, he "was going to blow it to the world's press", he said.
It was child's play to get into US military systems, McKinnon said.
Many were running Netbios over TCP/IP with blank or default passwords,
which allowed him to access-administrator privileges.
He admitted writing scripts to harvest passwords,
and to using password crackers to get into more protected systems.
Gaining secret access was clearly seductive. McKinnon speaks of "megalomaniacal" feelings
when he was deep inside systems. But he was not alone, he said.
By querying who else was connected and investigating IP addresses,
he found Chinese, European and other nationals visiting the same computer systems.
"At first I thought they might be offsite contract workers, but that was not the case," he said.
Once he was inside a network, especially a military network,
McKinnon found that other computer systems considered him a trusted user.
This was how he was able to get into the Pentagon's network.
"It was really by accident," he says.
The most secret system McKinnon said that he hacked was China Lake,
a facility that develops airborne weapons for the US Navy and Marine Corps.
He found little evidence of other-world natives or technology,
except for a spreadsheet that listed "non-terrestrial officers, ships' names and goods movements",
and a picture of what he said was a UFO with a perfectly smooth surface.
Would he do it again? "Never.
I would go through legitimate channels such as the Freedom of Information Act," he says.
The former systems administrator supported himself by driving a forklift truck
as he waited for the legal process to run its course.
The work dried up as employers grew unhappy with the attention the media focused on him.
He now lives on benefits.
McKinnon says National Hi-Tech Crime Unit officers told him
then a British court would probably give him six months' community service,
which he was prepared to accept. If extradited and convicted,
he faces 60 or more years in a US jail.
Hacker advises on how to protect your network
Gary McKinnon, who is fighting extradition to the US to face hacking charges,
offers CIOs and network administrators a few words of advice on network protection.