Kretsinger, a 24-year-old who used the moniker "Recursion," pleaded guilty to one count each of conspiracy and unauthorized impairment of a protected computer in a deal with prosecutors.

LulzSec, an offshoot of the international hacking group Anonymous, has taken credit for hacking attacks on government and private sector websites.

"I joined LulzSec, your honor, at which point we gained access to the Sony Pictures website," Kretsinger told the judge after entering his guilty plea.

He testified that he gave the information he got from the Sony site to other members of LulzSec, who then posted it onto the group's website and on Twitter.

Kretsinger flew from Decatur, Illinois, to Los Angeles for the hearing, and responded to the judge's questions calmly, with his hands clasped behind his back.

He and other LulzSec hackers, including those known as "Sabu" and "Topiary," stole the personal information of thousands of people after launching an "SQL injection" attack on the website, and ultimately caused Sony Pictures Entertainment more than $600,000 in damages, Assistant U.S. Attorney Eric Vandevelde said.

The plea agreement came a month after court documents revealed that Anonymous leader "Sabu," whose real name is Hector Xavier Monsegur, had pleaded guilty to hacking-related charges and provided the FBI with information on fellow hackers.

U.S. prosecutors and the FBI filed charges last month against five other suspected leaders of the international hacking group, all of whom were members of LulzSec, for computer hacking and other crimes.

Vandevelde would not comment on whether Kretsinger was also cooperating with authorities in exchange for leniency in sentencing, or if the Sabu case affected this one in any way.

The plea agreement is under seal, although Vandevelde said Kretsinger would likely receive substantially less than the 15-year maximum sentence he faces. He could also be forced to repay any damages.

His sentencing is scheduled for July 26. Neither Kretsinger nor his lawyer would comment after the proceedings.

Anonymous and its offshoots, including LulzSec and AntiSec, focused initially on fighting attempts at Internet regulation and the blocking of free illegal downloads, but have since taken on other targets including Scientology and the global banking system.

Anonymous - and LulzSec in particular - became notorious in late 2010 when they launched what they called the "first cyber war" in retaliation for attempts to shut down the Wikileaks website.

They attacked websites including MasterCard.com, which had tried to block payments to Wikileaks after apparent pressure from the U.S. government following the release of thousands of diplomatic cables.

(Reporting by Mary Slosson; Editing by Cynthia Johnston and Doina Chiacu)

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