A federal grand jury in Los Angeles has indicted a 20-year-old British citizen on charges related to attacks by the LulzSec hacking group on the Fox and PBS television networks and Sony's film and TV studio, authorities said on Wednesday.

Ryan Cleary, who is already jailed in the United Kingdom where he faces prosecution over similar charges, is accused of joining other members of LulzSec in harnessing compromised computers, known as a "botnet," to steal confidential information, deface websites or attack servers. He was indicted on Tuesday.

"Cleary is a skilled hacker. He controlled his own botnet, employed sophisticated methods and his broad geographic scope affected a large number of businesses and individuals," FBI spokeswoman Laura Eimiller said.

LulzSec, an offshoot of the international hacking group Anonymous, has taken credit for hacking attacks on government and private sector websites.

Anonymous and its offshoots, including LulzSec and AntiSec, initially focused on fighting attempts at Internet regulation and the blocking of free illegal downloads, but have since taken on such targets as Scientology and the global banking system.

The charges come just over two months after accused LulzSec hacker Cody Kretsinger pleaded guilty in U.S. District Court in Los Angeles to taking part in an extensive computer breach of Sony Corp's Sony Pictures Entertainment.

In March, court documents revealed that Anonymous leader "Sabu," whose real name is Hector Xavier Monsegur, had pleaded guilty to hacking-related charges and provided the FBI with information on fellow hackers.

According to the indictment released by the FBI, Cleary and his unnamed co-conspirators hacked into the computer systems of News Corp's Fox Entertainment Group and Sony Pictures Entertainment and stole confidential user information.

The indictment also charges Cleary and his co-conspirators of defacing the PBS website and launching "denial of service" attacks against an online gaming website and Britain's Serious Organized Crime Agency.

Cleary is charged with one count of conspiracy and two counts of unauthorized impairment of a protected computer. He faces a maximum sentence of 25 years in prison if convicted.

Eimiller said federal authorities would "allow the prosecution to take its course" against Cleary overseas before deciding whether to seek his extradition to the United States. He is next scheduled to be in court in the U.K. on June 25.

Anonymous, and LulzSec in particular, became notorious in late 2010 when they launched what they called the "first cyber war" in retaliation for attempts to shut down the WikiLeaks website.

They attacked websites including those of MasterCard Inc, which had tried to block payments to WikiLeaks after apparent pressure from the U.S. government following the release of thousands of diplomatic cables.