Matthew Keys, a 26-year-old deputy social media editor at Thomson Reuters, has been charged with assisting the hacking collective Anonymous in an attack on the Web site of The Los Angeles Times, the Justice Department said Thursday.

A federal indictment of Mr. Keys, formerly a Web producer at KTXL Fox 40, which, like The Los Angeles Times, is owned by the Tribune Company, said that he went by a user name of “AESCracked” and assisted in a cyberattack on the newspaper’s Web site. The attack reportedly allowed the group to gain access and alter a news feature.

The three-count indictment includes charges that Mr. Keys provided Anonymous with login information for computers owned by the Tribune Company. The indictment also states that he encouraged the hackers, with whom he worked from Dec. 10 to Dec. 15, 2010, to log on to the Tribune Company server “to make unauthorized changes to Web sites” owned by the company and “to damage computer systems” used at the Tribune Company.

A Los Angeles Times news article with the headline “Pressure Builds in House to Pass Tax-Cut Package” was renamed “Pressure Builds in the House to Elect CHIPPY 1337,” according to the indictment.

If convicted, Mr. Keys could face up to 10 years in prison for each substantive count and three years of supervised release and a fine of $250,000 for each count, the Justice Department said in a news release. A spokesman for Reuters said that the news organization was aware of the charges against Mr. Keys and that the alleged misconduct occurred before Mr. Keys joined Reuters in 2012. A spokesman for Tribune Company declined to comment.

The charges came as a shock in social media circles where Mr. Keys, considered a wunderkind of new media, cut a popular presence, including being named one of Time Magazine’s 140 best Twitter feeds. But the tsunami of social media also appeared to have taken a toll on Mr. Keys.

After posting more than 46,000 Twitter messages, Mr. Keys publicly took a break from the social media Web site. In an interview with Ad Week in July, he said Twitter had kept him up at night. “I got sucked into that. I loved it. I still love it. But at some point you have to take a break,” Mr. Keys said. (In a Twitter post on Thursday, Mr. Keys again said he intended to take a break.)

The length of his potential sentence reignited online protests on Thursday over the way federal prosecutors approached the Internet. Those protests from open Internet proponents like the Electronic Frontier Foundation, exploded in January after the computer programming prodigy Aaron Swartz, also 26 and facing federal charges related to hacking, committed suicide.

The charges against Mr. Keys came as other media organizations were facing computer threats. Chinese hackers have compromised the computer systems of several major United States media organizations, including The New York Times and The Wall Street Journal. The Ministry of National Defense of China has denied any involvement in the attacks.

On Wednesday, President Obama met with chief executives to discuss digital security legislation. In an interview with ABC News on Wednesday, he acknowledged the “ramping up of cybersecurity threats.”

Anonymous, a nebulous and global collective of so-called hactivists, often use computers in protesting or supporting political causes. The group demanded Christmas dinner be provided to Pfc. Bradley Manning, the former Army intelligence officer arrested in 2010 on accusations of leaking classified documents to WikiLeaks.

In a Twitter message posted last year, Hector Xavier Monsegur, a hacker known as “Sabu” who led a hacking collective and worked as an F.B.I. informant, accused Mr. Keys of playing a part in hacking into The Los Angeles Times.

Mr. Keys has written about Sabu and Anonymous for Reuters and been associated with hacking groups in the past, including in a Gawker article that identified him as a “journalist who infiltrated” Anonymous.

“I identified myself as a journalist during my interaction with top-level Anonymous hackers,” Mr. Keys wrote on his personal blog in response to the Gawker article.

The charges against Mr. Keys were first reported by The Huffington Post.