Gary McKinnon, a hacker who broke into US government computer systems seeking evidence of alien life, has failed in his latest efforts to block extradition to the US to face trial.

On Friday, the High Court ruled the extradition of McKinnon, whose hacking exploits have drawn high-profile attention from UK Prime Minister Gordon Brown and celebrities such as David Gilmour of Pink Floyd, should proceed. Karen Todner, McKinnon's attorney, said they will lodge an appeal within 28 days.

McKinnon's attorneys had asked the court to review a refusal by the Director of Public Prosecutions (DPP) for England and Wales to prosecute the him in the UK British prosecutors maintain that the US wants jurisdiction and that most evidence and witnesses are in the US

McKinnon had also asked the court to review his extradition order, which was approved by the UK government in July 2006, on the basis of his diagnosis with Asperger Syndrome, a neurological disorder characterised by obsessive behaviour and deficiencies in social interaction.

He faces up to 60 years in prison for hacking into 97 US military and NASA computers between February 2001 and March 2002. He was indicted in 2002 in the US District Court for the Eastern District of Virginia.

While in the UK, McKinnon has freely admitted to hacking the computers using a program called "RemotelyAnywhere," a remote access tool. He has said that many of the computer systems still had their default passwords, which is generally considered a poor security practice, and that other passwords were easy to obtain.

McKinnon contends he didn't harm the computer but was merely searching for proof of the existence UFOs.

The US military contends that McKinnon hacked 97 military computers and caused $800,000 (£487,000) of damage, and deleted critical files from its computers, which hampered its efforts after the 11 Sept., 2001, terrorist attacks.