At a hearing at Bow Street Magistrates' Court on Wednesday, McKinnon's lawyers claimed that he could be detained indefinitely by the US authorities. McKinnon is charged with illegally accessing 97 US government computers and causing US$700,000 worth of damage over a 12-month period starting in February 2001.
Last year, McKinnon told ZDNet Australia's sister site ZDNet UK that he had accessed the computers because he was looking for evidence that the US had found extraterrestrial life. He denied causing serious damage.
Lawyers for the defence told the court that the US could choose to treat McKinnon under its "military order No. 1," which allows suspected terrorists to be tried under military law.
District Judge Nicholas Evans, who is hearing the case, ruled that the extradition request would be denied unless American officials could guarantee they would not prosecute McKinnon under the order.
"All you have to do is satisfy the court he is not at risk," said Evans, according to The Guardian. "And if you cannot, then there is a problem."
The case is due to resume on 14 March.
ZDNet UK's Graeme Wearden reported from London. For more coverage from ZDNet UK, click here.
