A federal grand jury hit 13 members of the online hacktivist group "Anonymous" with indictments on Thursday for conspiracy to intentionally cause damage to protected computers.

The 13 accused people were allegedly part of "Operation Payback," which went after websites of the U.S. Copyright Office, MasterCard, Visa, Bank of America, Recording Industry Association of America (RIAA), Motion Picture Association of America (MPAA) and law firms, noted CBS News.

According to court papers, Operation Payback targeted those who “opposed its stated philosophy of making all information free for all, including information protected by copyright laws or national security considerations.”

Prosecutors claim that Anonymous used massive denial-of-service (DDoS) attacks against their victims with Low Orbit Ion Cannon software, which floods a web site's servers with too many requests and knocks it off the web, reports Reuters.

The DDoS attacks supposedly began after the file-sharing sites The Pirate Bay and Limewire were taken off the web by authorities in 2010, although The Pirate Bay is back up.

Some of the attacks were allegedly in response to the U.S. government's harassment of Wikileaks and its founder Julian Assange.

Sources: CBS News and Reuters