Edmund Lawson, who is defending McKinnon, told a hearing at London's High Court that McKinnon faced up to 60 years' imprisonment if he was convicted in the U.S., where he could be tried under its antiterrorism legislation. Thehearing began on Tuesday.
McKinnon isin 2001 and 2002, causing $700,000 worth of damage. In an admitted accessing the computers as part of his search for evidence of extraterrestrial life, but denied deliberately doing any damage.
In May 2006, ato face these charges.
Lawson said that McKinnon had been offered a deal by U.S. authorities, under which he would receive a shorter sentence if he stopped fighting extradition. This offer had been rejected, and constituted an "improper approach" to McKinnon, Lawson said.
Representing the U.S. authorities, Max Summers told the court that the U.S. was not able to refute this claim immediately and would need an adjournment to consider it.
The High Court appeal case was adjourned on Wednesday afternoon, and the judges will now deliberate on whether this new evidence can be considered.
McKinnon was taken ill as his appeal against extradition continued. According to those close to McKinnon, he suffered heart palpitations on Wednesday. "The case has all become too much for him," a friend told ZDNet UK.
If he loses his U.K. appeal, McKinnon may try to appeal to the European Court of Human Rights, although this move may be blocked by the High Court.
Colin Barker reported for ZDNet UK in London.