Gary McKinnon, the Briton who is facing extradition to the U.S. for hacking into NASA's computers, is to appeal the deportation on Monday.

McKinnon's appeal will be heard in a two-hour session in the House of Lords.

The former systems administrator says he spent two years hacking into a number of U.S. government systems looking for evidence of extraterrestrial life. He is accused of illegally accessing computers belonging to the U.S. Army, Navy, Air Force, NASA, the Department of Defense 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 says that 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. He says that U.S. representatives then pursued the maximum sentence available, and said he would be "turned over to New Jersey authorities to 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 of an appeal at the European Court of Human Rights, and have the extradition put on hold.

If he wins the appeal, he says the extradition will be thrown out. He could then still face charges through the U.K. justice system and it would be unlikely he could ever leave the country for fear of further action.

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 for extraditions to the United States and said he will "spend a lot of time" trying to get 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 or any damage it might have done to request his extradition.

McKinnon was arrested in 2002. During his hacking attempts, he claims that he succeeded in finding evidence of extra-terrestrial life in the form of images and spreadsheets.

"I saw photos in space of things that didn't look man-made," McKinnon said. "And I saw an Excel spreadsheet with non-terrestrial officers with their names and ranks. That makes me think there's a space force being developed in secret."