Jeremy Hammond was arrested in a major federal sweep last year on charges of computer hacking conspiracy, computer hacking, and conspiracy to commit access device fraud.
The self-described hacktivist pled guilty to these counts in court on Tuesday, according to the Associated Press.
"As part of each of these hacks, I took and decimated confidential information stored on computer systems websites used by each of the entities," Hammond told a judge in federal court in Manhattan, according to the Associated Press. "For each of these hacks, I knew what I was doing was against the law."
The feds nabbed Hammond, 28, and a handful of other alleged hackers after an insider named Hector Xavier Monsegur, or Sabu, ratted them out. While the authorities were going after hackers in the Lulzsec hacking group at the time, they also picked up Hammond, who they said was part of an Anonymous-affiliated hacktivist group called Antisec.
Antisec took responsibility for hacking into security think tank Strategic Forecasting, or Stratfor, in December 2011. One of the group's claims was the theft 200GB worth of data, including e-mails and clients' credit card information.
Days after the hack, the group published 860,000 e-mail addresses and 75,000 unencrypted credit card numbers on the Web. The FBI also claimed that at least $700,000 worth of unauthorized charges were made to credit card accounts stolen in the hack. Hammond was accused by the feds of being one of the kingpin hackers allegedly involved in this massive cyberattack.
"Jeremy has taken responsibility for what he's done, but he should not face such a harsh sentence for an act of protest from which he did not personally benefit," Hammond's brother, Jason Hammond, said in a statement, according to the Associated Press.
Hammond will be sentenced on September 6; he faces up to 10 years in prison.