LulzSec hacker who switched sides to help US foil attacks to leave jail after being sentenced to time served

An admitted computer hacker who helped the FBI thwart hundreds of cyberattacks on government and corporate computer systems will be freed from prison.

Hector Xavier Monsegur was sentenced yesterday in Manhattan to the time he had already served - seven months.

Monsegur infiltrated the servers of major corporations but switched sides and helped the US government disrupt hundreds of cyberattacks on Congress, Nasa and other sensitive targets, according to federal prosecutors.

New York prosecutors detailed the cooperation of Monsegur in court papers while asking a judge to reward him with leniency at his sentencing. They credited Monsegur with helping them cripple Anonymous, the notorious crew of hacktivists who stole confidential information, defaced websites and temporarily put some victims out of business.

Working around the clock with FBI agents at his side, Monsegur "provided, in real time, information about then-ongoing computer hacks and vulnerabilities in significant computer systems", prosecutors wrote. The FBI estimates he helped detect at least 300 separate hacks, preventing millions of dollars in losses.

Court papers say Monsegur first began hacking in a Manhattan apartment in the early 2000s. His aim then was to steal credit card information, then sell it or use it to pay his own bills.