The hacking group also said it hit other websites run by News International, News Corp.

WSJ: Hackers Claim 'Sun' Site Hit

The alleged hacking was significant because the documents came from the government-run Public Access to Court Electronic Records, or PACER, which typically charges a fee, which was 8 cents a page in 2009.

CNN: Internet prodigy, activist Aaron Swartz commits suicide

The operation is being run alongside Scotland Yard's Operation Weeting, which is looking into phone hacking.

BBC: John Terry