Gary McKinnon has begun his fight against extradition to the US, where he faces a possible sentence of 70 years in jail and a fine of up to $250,000. The alleged hacker argues that he should be tried in the UK.

McKinnon, 39, from Wood Green in north London, was charged at Bow Street Magistrates' Court with breaking into 97 US government computers over a period from February 2001 to March 2002. The case was adjourned until 18 October.

Mark Summers, representing the US government, said in court that McKinnon's hacking was "intentional and calculated to influence and affect the US government by intimidation and coercion".

McKinnon claims that he was looking for evidence of a government cover-up of UFOs.

District Judge Nicholas Evans ordered him to report to his local police station twice weekly and banned him from using computers and the internet.

Paul McNulty, US attorney for the Eastern District of Virginia, described the McKinnon case as the "biggest military computer hack of all time", and claimed that the damage caused is an estimated $700,000.

McKinnon is alleged to have accessed 53 computers at the US Army, 26 at the US Navy, 16 at Nasa, one at the US Department of Defense and one at the US Air Force after finding a single open system.

Prosecutors also claimed that McKinnon installed commonly available hacking tools on some computers, and that some important networks had to be taken down to clean up the systems.