Thirteen alleged members of the loosely organized hacker collective known as Anonymous were indicted Thursday in connection with a series of online attacks on US companies and trade groups.

The indictment unsealed in Alexandria, Virginia, charged the 13 with attacks between September 2010 and January 2011 on the Motion Picture Association of America, Recording Industry Association of America, Visa, Mastercard, Bank of America and others.

The defendants were charged with organizing denial of service attacks aimed at shutting down the websites of the targets known as "Operation Payback."

The targets were chosen for their stand on piracy and copyright enforcement after the discontinuation of Pirate Bay, and the financial institutions later for ending transactions that allowed funds to be raised for Wikileaks founder Julian Assange.

The 13 "planned and executed a coordinated series of cyber-attacks against victim websites by flooding those websites with a huge volume of irrelevant Internet traffic with the intent to make the resources on the websites unavailable to customers and users of those websites," the indictment said.

Those named in the indictment were Dennis Owen Collins, Jeremy Leroy Heller, Chen Zhiwei, Joshua Phy, Ryan Russel Gubele, Robert Audubon Whitfield, Anthony Tadros, Geoffrey Kenneth Commander, Austen Stamm, Timothy Robert McLain, Wade Carl Williams and Thomas Bell.

Anonymous is a loose-knit group hacker activists, or "hacktivists," who have taken credit for scores of online attacks over the past few years.

The attacks range from the nuisance-like -- the FBI and Justice Department websites were back up within a few hours -- to the truly damaging involving the loss of data and the exposure of private financial information.