The Big Question: What exactly did Gary McKinnon do wrong, and should he be extradited?

Why are we asking this now?

Because Gary McKinnon has been fighting the United States' plans to have him extradited on hacking charges for the best part of seven years.

But last week the 43-year-old lurched ever closer towards being handed over to American law enforcement officials after losing his latest High Court battle to have him stay in the UK. After weeks of deliberation, two High Court judges went against McKinnon on two legal points he had hoped might allow him to be tried in the UK rather than in the States, where he faces up to 60 years in a maximum security jail.

So what exactly is he accused of doing?

The US accuses him of being responsible for the "biggest military hack of all time", although his supporters say that is over-hyped rhetoric from US prosecutors who are determined to see him jailed in the States and therefore want to emphasise the severity of his crimes. What is not in dispute (because he admits it) is that, between February 2001 and March 2002, Mr McKinnon hacked his way into 97 US military computers, including terminals owned by the US Navy, the Pentagon and Nasa. The US claims that he deleted critical files from operating systems that led to the near-complete shut down of the US Army's Washington network, costing some $700,000.

How did he do it?

Remarkably easily, in fact. When The Independent interviewed Mr McKinnon last year he described how breaking into American military computers, even after the September 11 attacks, was surprisingly simple because many staff at government facilities simply left their default passwords in place and were therefore incredibly easy to crack. But Mr McKinnon disputed the suggestion that he caused any damage.

"I wouldn't call what I did an attack," he said. "It was more like probing, snooping around and leaving messages – what hackers call 'hactivism'. Attack suggests some sort of malicious intent, which there simply wasn't." American officials, however, see things very differently, with one New Jersey prosecutor promising to see the north Londoner "fry" for his hacking.

How did he get caught?

Once again, remarkably easily. Mr McKinnon did little to hide his IP address (the individual identity code that each computer has) and even hacked using his own email registered to his flat in Wood Green in north London. McKinnon's supporters argue that this is proof of how he had no malicious intent. If he was really a dangerous cyber-hacker, they argue, he would have covered up his tracks.

So why did he do it?

Part of it was political – the messages he left on hacked military computers ranged from posts like "your security is crap" to anti-American slogans which, in the febrile atmosphere post-9/11, obviously didn't go down very well with US officials. But what really motivated Mr McKinnon was a conspiracy theorist's belief that America's military had evidence of extraterrestrial life and, specifically, UFOs.

Isn't that quite strange behaviour?

As Mr McKinnon's case rumbled on in Britain's law courts he was eventually diagnosed with having Asperger's Syndrome, a form of autism which, his supporters say, led to compulsive and obsessive behaviour at the time of his hacking. When he was caught, Mr McKinnon was spending up to 18 hours a day on his computer, obsessed with the idea of finding extraterrestrial life. His lawyers maintain that far from the dangerous cyber-warrior American prosecutors portray him as, he is in fact an eccentric and vulnerable individual who should not have to go through the trauma of being imprisoned thousands of miles from home.

What is the situation with the legal arguments?

Mr McKinnon's lawyers have been to the courts numerous times before, but the latest High Court battle, which they lost last week, centred around two arguments.

The first was that extraditing McKinnon to the US, where he faces a maximum sentence of 60 years in a so-called "supermax" prison, would be a breach of his human rights because of his Asperger's. The second was to oppose a decision by Keir Starmer QC, the Director of Public Prosecutions, who declined to have McKinnon prosecuted in Britain rather than the US. On both counts courts sided with the Government.

His lawyers have promised to appeal to the newly created Supreme Court within the next 28 days and, if necessary, to the European Court of Human Rights. So Mr McKinnon is not going to be clad in irons just yet.

So is his extradition a foregone conclusion?

If the appeals fail then, according to the Government, it is. Home Secretary Alan Johnson has claimed that stopping McKinnon's removal would be in breach of the extradition treaty signed between the US and Britain and would therefore be illegal. But a number of legal minds have disputed this position, including Lord Carlisle – the Government's own terror adviser – and two barristers from Cherie Blair's Matrix chambers, who believe the Home Secretary is entitled to use his discretion and intervene. Both the Conservatives and the Liberal Democrats support the idea of Mr McKinnon being tried in the UK and, yesterday, Peter Hain became the first cabinet minister to break ranks with Mr Johnson by stating that it would be better to prosecute him "in a British context".

Isn't Britain's extradition treaty something of a sore point as well?

McKinnon's backers are generally made up of two camps. The first are those who believe he is a vulnerable person who did something stupid without malicious intent and is being disproportionately pursued by the United States, with Britain's blessing, because they are embarrassed by what he did and want to send a strong signal to other "hactivists". A second camp, however, sees his potential extradition as part of a wider policy by Britain of kowtowing to America without expecting reciprocity from across the Atlantic.

So what's wrong with the treaty?

Detractors of our extradition treaty – which, unlike Parliament, took Congress years to sign – say it is weighted against Britain because it removes the requirement for the US to provide prima facie evidence when requesting the extradition of any UK citizen, but still requires the UK to do so. Campaigners also believe that, compared with other British subjects who have been extradited to the US, Mr McKinnon has had little support from the Government. They contrast his treatment to that of the so-called NatWest Three – a trio of bankers who were later found guilty of fraud related to the Enron scandal. As their extradition loomed Tony Blair personally lobbied to make sure they received bail on arrival in the US and would serve out their sentences in the UK. Britain has only just indicated that it may be willing to do the same for Mr McKinnon after seven years of campaigning.

So should Mr McKinnon be sent to stand trial in the US?

Yes...

*He may say he didn't mean to cause damage with his hacking, but he did and should take responsibility for his actions

*He has admitted to the hacking, which could have been catastrophic for American security

*Fears over the punishment he might face in the US are exaggerated

No...

*The United States are treating a harmless eccentric who made a non-malicious mistake like a terrorist

*The treaty between the US and UK is unfair and should not be used

*McKinnon's self-confessed crimes may have impacted on the US, but they were committed on UK soil and hence he should be prosecuted here