Updated

A French judge has issued an arrest warrant for disgraced U.S. cyclist Floyd Landis for allegedly hacking into a lab computer at a facility run by the country's anti-doping agency, the agency's head told Reuters.

Landis, whose surprise victory at the 2006 Tour de France was stripped after he tested positive for synthetic testosterone, was banned from cycling for two years and only returned to the sport last January.

He now faces far a more serious inquiry, according to prosecutors in the Paris suburb of Nanterre.

French judge Thomas Cassuto is seeking to question Landis about computer hacking dating back to September 2006 at the Chatenay-Malabry lab, which uncovered the abnormally elevated testosterone levels in Landis' urine samples.

French officials filed a criminal complaint in 2006 over the hacking, which they said was designed to discredit the drug tests they had conducted on Landis. No charges were filed against the 34-year-old at the time.

The American cyclist challenged the drug test results before an arbitration hearing in California -- claiming that computer files were mishandled and erased -- but was still stripped of his Tour de France title.

"Landis used the hacked files for his defense, that's how we discovered the whole scheme," said Pierre Bordry, France's anti-doping chief. "He wanted to show that the lab made mistakes in the handling of the tests."

Landis did not immediately respond to a phone call and e-mail seeking comment.

Judge Cassuto issued the warrant Jan. 28 because Landis did not respond to a summons in November, Bordry said.

"Apparently the judge traced the case back to the beginning," Bordry said. "I can't say I'm happy with this news because I would have preferred there was no Landis case."

Cassuto also issued a national warrant for Arnie Baker, a retired doctor and longtime Landis coach and adviser, the prosecutor's office said.

After discovering the hacking, the French lab upgraded security to protect its computer systems.

Landis' urine samples were tested at the lab and found to contain elevated testosterone-to-epitestosterone levels, less than a week after he won the Tour de France.

On July 20, 2006, the Tour's 17th stage, Landis started more than eight minutes behind leader Oscar Pereiro after losing the yellow jersey to the Spaniard the previous day. But Landis produced an amazing ride during the mountainous stage to cut Pereiro's lead to 30 seconds before taking the title.

Landis' samples taken after that stage revealed a testosterone/epitestosterone ratio of 11:1 — nearly three times the 4:1 limit.

The Chatenay-Malabry lab is accredited by the International Olympic Committee and World Anti-Doping Agency. It helped develop tests for the endurance-enhancing drug EPO.

Landis returned to competition at the Tour of California last year. He recently competed in a minor race staged in New Zealand.

The Associated Press contributed to this report.