LulzSec had more than one mole in its group. Sabu was not the only one that helped the FBI bring down the group.

Three different informants were involved in the investigation and redacted documents indicate that two of whom were members of the organization.

Information obtained by both Sabu and an unidentified informant allowed the FBI to obtain warrants against other LulzSec and Anonymous suspects. The informants are only referred to as CW1 and CW2 (confidential witness-1 and confidential witness-2).

If you recall, LulzSec was semi-famous between May and June 2011 with its attacks on such sites as:
Fox, Sony, FBI-affiliated security outfits such as Infragard and HB Gary Federal, the US Senate, the Arizona State Police, the CIA and the UK's Serious Organised Crime Agency.

Targets such as entertainment sites were firms opposing file-sharing, while security sites were hacked in an effort to embarrass them.

Jeremy Hammond (AKA Anarchaos), 29, of Chicago, Illinois, another hacker arrested faced a tougher sentence than most. While others were sentenced to between 24 to 32 months, Hammond drew a ten year sentence for hacking and publishing personal info from a hack on security intelligence outfit Stratfor that took place in December 2011.