His attacks between 2001 and 2002 allegedly shut down the US Army district responsible for protecting Washington, and cleared logs from computers at the Naval Weapons Station Earle in New Jersey that tracks the location and battle-readiness of navy ships. That last attack knocked out the station's entire network of 300 computers. NASA and privately owned computers were also damaged, prosecutors said, putting the total cost of his online activities at $US900,000.

At the time of his indictment, US prosecutor Paul McNulty said McKinnon pulled off "the biggest hack of military computers ever - at least ever detected". In his defence, McKinnon, known online as SOLO, said he was trying to expose security weaknesses and uncover evidence of UFOs. "I was a man obsessed," McKinnon wrote on The Guardian newspaper's website last year, describing a year spent trying to break into US military systems: eight hours a day at a computer in his girlfriend's aunt's house while unkempt, drinking beer and smoking marijuana.

In interviews, he claimed that his hacking uncovered photographic proof of alien spacecraft and the names and ranks of "non-terrestrial officers". Prosecutors accuse him of deliberately trying to intimidate the US Government by tearing through its networks. They pointed to a note written by McKinnon - and left on an army computer - attacking US foreign policy as "akin to government-sponsored terrorism".

"It was not a mistake that there was a huge security stand-down on September 11 last year," he wrote. "I am SOLO. I will continue to disrupt at the highest levels." McKinnon was caught in 2002 after some of the software used in the attacks was traced to his girlfriend's email account. The US sought his extradition, a move his lawyer Claire Anderson claimed today was motivated by the Government's desire to "make an example" of a man who humbled officials in Washington by hacking into their systems using off-the-shelf office software and a dial-up modem. Aspects of American cyber-security had been shown up as "really shameful," with some computers not even password-protected, said Graham Cluley, a security consultant with Sophos PLC.

He said the United States appeared to be pursuing McKinnon in an effort to flexing its legal muscle to the hacking community, which has watched the case with interest. "The overriding message is: you shouldn't mess with American government and military computers, particularly right after September 11," Cluley said.

McKinnon's lawyers had hoped to hold any trial in Britain, saying he could be dragged before a military tribunal or even end up at the Guantanamo Bay military prison camp in Cuba. Should McKinnon be extradited, he would face trial in Virginia and New Jersey on eight charges of computer fraud. Each charge potentially carries a sentence of up to 10 years in prison and $US250,000 in fines. However, US sentencing guidelines would probably recommend a much lighter sentence.

AP