Hacker Gary McKinnon is facing a long wait to discover if he is to face charges.

The US has 60 days by law to prove its case for extradition from the date it files its claim. It has not yet done so but has started to appoint a grand jury to file the claim.

McKinnon, a 36-year-old unemployed computer programmer from north London, is believed to have caused damage estimated at more than half a million during attacks on the US Army, Navy and on Nasa.

He operated under the code name Solo and was arrested by the UK Hi-Tech Crime Unit.

"Solo has been around for a while but has never done anything on this scale before," said Matt Tomlinson, business development director at MIS Corporate Defence Solutions. "He's respected in the hacker community and we know other hackers have benefited from the knowledge he has passed on."

As for the attacks themselves, it seems they may not have been as advanced as has previously been reported.

"In my opinion he was not a professional," said Bart Vansevenant, director of European security strategy at Ubizen.

"It's frightening to see what he did with a very common tool. He was using a standard port scanner looking for a system administrator who hadn't installed a publicly available patch.

"He wasn't concealing his IP address or using other identities, another sign of an amateur," Vansevenant added.

In a statement, McKinnon's lawyers expressed surprise that the British government had not charged him but had allowed US authorities to pursue extradition.

"We can only assume that the motivation for this conduct is political and that it is proposed to make an example of Mr McKinnon. We wish to emphasise ... that he has no terrorist links whatsoever," the statement said.

If the extradition is successful McKinnon will be tried in Virginia and New Jersey. US authorities want to charge McKinnon with seven counts of computer fraud. If found guilty, he could be fined up to $1.75m (£1.10m) and sentenced to up to 70 years in jail.

The Washington Times has reported that the US District Court for the Eastern District of Virginia is nicknamed 'The Rocket Docket' and has one of the most conservative jury pools of any federal court.

Its US attorney Paul McNulty has played a leading role in high-profile cases, including those of American Taliban member John Walker Lindh; Zacarias Moussaoui, the first person to face criminal charges in the 11 September attacks; and convicted spy Robert Hanssen.

Fellow US attorney Christopher Christie described McKinnon's hacking attacks as "a grave intrusion into a vital military computer system at a time when we, as a nation, had to summon all of our defences against further attack."

McKinnon is said to have caused more than $900,000 (£567,000) worth of damage in 92 attacks between March 2001 and March 2002. After gaining entry, he used a software programme called RemotelyAnywhere to monitor network traffic and delete files.

He is thought to have downloaded hundreds of user passwords, and in several cases destroyed critical files, making computers unable to function.

In one incident he shut off more than 1,000 military users in the Washington area from their network for three days. He is also said to have caused $290,000 worth of damage to a US Navy station in New Jersey.