A British man accused of being behind the largest ever hack of US government computer networks could end up at Guantanamo Bay, his lawyer has claimed.
Gary McKinnon, from London, denies causing $700,000 (£400,000) damage to military and Nasa systems in 2001-2.
Bow Street Magistrates' Court was told the 40-year-old feared a prosecution might take place under US anti-terror laws if it agreed to his extradition.
The US said Mr McKinnon had assurances he would be tried in a federal court.
But defence lawyers said his human rights could be breached if he was sent to the US.
Mr McKinnon was remanded on bail until 10 May when District Judge Nicholas Evans will rule whether the extradition will go ahead.
Much of the hearing was taken up with argument over whether Mr McKinnon would be subject to Military Order Number One - a legal procedure which enables the president to specify that suspects can be detained indefinitely.
Mark Summers, representing the US government, said there was no precedent to suggest the US would breach its promises, and the court should take on "faith" the undertaking.
Defence lawyer Edmund Lawson said the US Embassy in London had provided an "unsigned and anonymous" diplomatic note and said Mr McKinnon was still "vulnerable" to such an order.
He said the US had not given a guarantee he will face a federal court trial.
"The US government wants to extract some kind of species of administrative revenge because he exposed their security systems as weak and helpless as they were," Mr Lawson added.
Mr McKinnon is accused of hacking into computers in 14 states, including at the Pentagon and naval weapon station Earle.
At an earlier hearing his lawyers suggested his actions were not malicious - he had been trying to expose lax computer security and access what he believed was withheld information about UFOs.