Kretsinger, 23, was arrested in September 2011 by the F.B.I. He was charged with conspiracy and the unauthorized impairment of a protected computer.
He pled guilty to both charges, as part of a plea deal.
“I joined LulzSec, your honor, at which point we gained access to the Sony Pictures website,” Kretsinger, who went by the hacking alias “Recursion,” told the judge.
LulzSec is considered to be a spinoff of Anonymous, the hacker and activist group that operates online.
Earlier this month, the FBI arrested several members of LulzSec using intelligence gained by interrogating “Sabu”, the group’s nominal leader, but a group claiming to be LulzSec recently hacked the email database of CSS Corp.
In June, members of LulzSec allegedly hacked into SonyPictures.com and compromised the personal information of more than 1 million users. While the group did not copy the information of all 1 million people, it did gain access to thousands of records
Sony Pictures later notified 37,500 users that their personal information might be at risk.
Kretsinger was apparently not involved in a hack against the Sony PlayStation Network, which cost the company $171 million and took the service offline for 77 million PlayStation Network members for a total of six weeks. The Sony Pictures hack cost Sony Pictures $600,000 in damages.