The US government has unsealed charges against two Russian spies and two criminal hackers for allegedly pilfering 500 million Yahoo user accounts in 2014,
The indictments, announced at a news conference in Washington on Wednesday, represent the first time the US government has criminally charged Russian officials for cyber offences.
The content of at least 30 million accounts were accessed as part of a spam campaign and that at least 18 people who used other internet service providers, such as Google, were also victimised, the government charged.
The officers of the FSB, Russia's Federal Security Service, which is a successor to the KGB, were identified as Dmitry Dokuchaev and his superior, Igor Sushchin, the government said.
Alexsey Belan, who is on the list of most-wanted cyber criminals, and Karim Baratov, who was born in Kazakhstan but has Canadian citizenship, were also named in the indictment.
The Justice Department said Baratov was arrested in Canada on Tuesday and that his case is now pending with Canadian authorities.
Belan was arrested in an European country in June 2013 but escaped to Russia before he could be extradited to the United States, according to the Justice Department.
The 47-count indictment includes conspiracy, computer fraud and abuse, economic espionage, theft of trade secrets, wire fraud, access device fraud and aggravated identify theft.
The charges are not related to the hacking of Democratic emails that took place during the 2016 US presidential election. Intelligence agencies have said they were carried out by Russia in order to help the campaign of Republican President Donald Trump.
Yahoo said, when it announced the then-unprecedented breach last September, that it was working with law enforcement authorities and believed the attack was state-sponsored.
The company announced a still-larger breach in December that occurred in 2013 and affected one billion accounts, though it has not linked that intrusion to the one in 2014.
The hacking conspiracy, which began as early as 2014, allowed Belan to use his relationship with the Russian spy agency and access to Yahoo's network to engage in financial crimes.