McKinnon's appeal will be heard in a two-hour session in the House ofLords.
The former systems administrator says he spent two years hacking into anumber of U.S. government systems looking for evidence ofextraterrestrial life. He is accused of illegally accessing computersbelonging to the U.S. Army, Navy, Air Force, NASA, the Department ofDefense as well as a number of private companies.
Among his hacking tools was a perl script which tied together projects from other people.
U.S. prosecutors have acted angrily to McKinnon's actions. McKinnon saysthat U.S. authorities offered him a plea bargain with a sentence of three to four years, but that they were not prepared to guarantee that figure. Hesays that U.S. representatives then pursued the maximum sentenceavailable, and said he would be "turned over to New Jersey authoritiesto see him fry".
The maximum sentence is likely to be life imprisonment.
His case on Monday is based around the way in which the plea bargaining process was carried out.
McKinnon told SCMagazineUK: "It was very threatening behavior. I'm being treated as some kind of terrorist".
McKinnon denies deliberately causing any damage but he said: "I absolutely regret doing it".
The U.S. government claims McKinnon caused $700,000 worth of damage.
If McKinnon loses the appeal, he says he will use his final chance ofan appeal at the European Court of Human Rights, and have theextradition put on hold.
If he wins the appeal, he says the extradition will be thrown out. Hecould then still face charges through the U.K. justice system and itwould be unlikely he could ever leave the country for fear of furtheraction.
The decision is likely to come in three to four weeks.
McKinnon told SCMagazineUK that he had some hopes of success. "My chances are the best they've ever been," he said.
McKinnon said that if he wins, he hopes it will set a precedent forextraditions to the United States and said he will "spend a lot of time" trying toget the Extradition Treaty changed.
Under the terms of the treaty, which came into being in 2003, the U.S.government has not had to show any evidence of McKinnon's hacking orany damage it might have done to request his extradition.
McKinnon was arrested in 2002. During his hacking attempts, he claims that he succeeded in findingevidence of extra-terrestrial life in the form of images andspreadsheets.
"I saw photos in space of things that didn't look man-made," McKinnonsaid. "And I saw an Excel spreadsheet with non-terrestrial officerswith their names and ranks. That makes me think there's a space forcebeing developed in secret."