By Pamela Brown, Scott Glover and Mary Kay Mallonee CNN

WASHINGTON (CNN) -- The Department of Justice announced Wednesday that four people -- including two officers of the Russian Federal Security Service (FSB) -- have been indicted in connection to a massive hack of Yahoo information.

The hack, which the DOJ said was initiated in January 2014, affected at least 500 million Yahoo accounts. Some of the stolen information was used to "obtain unauthorized access to the contents of accounts at Yahoo, Google and other webmail providers, including accounts of Russian journalists, US and Russian government officials and private-sector employees of financial, transportation and other companies," the DOJ said in a statement.

The officers of the FSB -- Russia's successor to the Soviet Union's KGB -- were identified as Igor Anatolyevich Sushchin, 43, and Dmitry Aleksandrovich Dokuchaev, 33. The two allegedly conspired with Russian national Alexsey Alexseyevich Belan, aka "Magg," 29, and Karim Baratov, aka "Kay," "Karim Taloverov" and "Karim Akehmet Tokbergenov," 22, who is a resident of Canada.

Dokuchaev was arrested in a Russian sweep in December and accused of spying for the US.

"The criminal conduct at issue -- carried out and otherwise facilitated by officers from an FSB unit that serves as the FBI's point of contact in Moscow on cybercrime matters -- is beyond the pale," acting Assistant Attorney General Mary McCord said at a news conference in Washington.

Hackers stole data that included names, email addresses and passwords -- but not financial information, according to Yahoo's announcement regarding the breaches.

Yahoo CEO Marissa Mayer publicly thanked US authorities Wednesday, saying she was "very grateful" to the FBI and DOJ.

The San Francisco FBI office has scheduled a news conference for later Wednesday afternoon on undisclosed topics.

Yahoo has been breached at least twice, and the company previously said a September 2014 breach was state-sponsored but declined to identify who it believed was responsible.

The announcement of another cyberintrusion by Russian hackers comes at a time of delicate relations between the US and Russia.

The Yahoo hack is the latest cyberattack that US authorities have blamed on Russia, a nation with which President Donald Trump's new administration has sought to foster warmer relations.

Previous attacks US authorities have said Russian hackers perpetrated exposed the emails of Hillary Clinton's campaign chairman, John Podesta, and the internal workings of the Democratic National Committee.

This story has been updated to reflect new developments.

CNN's Eugene Scott and Theodore Schleifer contributed to this report.

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