The two FSB officers were named as Dmitry Dokuchaev and his superior, Igor Sushchin. The two hackers named were Alexsey Belan and Karim Baratov. The Yahoo! leak in question was one which resulted in credentials of 500 million accounts being compromised in 2014.
The indictments were announced at a press conference in Washington DC.
Baratov, who holds Canadian citizenship, was arrested on Tuesday (14 March) by Canadian authorities.
"The defendants used unauthorised access to Yahoo!'s systems to steal information from about at least 500 million Yahoo! accounts and then used some of that stolen information to obtain unauthorised access to the contents of accounts at Yahoo!, Google and other webmail providers, including accounts of Russian journalists, U. and Russian government officials and private-sector employees of financial, transportation and other companies," the DoJ announced.
"One of the defendants also exploited his access to Yahoo!'s network for his personal financial gain, by searching Yahoo! user communications for credit card and gift card account numbers, redirecting a subset of Yahoo! search engine Web traffic so he could make commissions and enabling the theft of the contacts of at least 30 million Yahoo! accounts to facilitate a spam campaign."
Attorney-General Jeff Sessions said: "Cyber crime poses a significant threat to our nation’s security and prosperity, and this is one of the largest data breaches in history.
"But thanks to the tireless efforts of U. prosecutors and investigators, as well as our Canadian partners, today we have identified four individuals, including two Russian FSB officers, responsible for unauthorised access to millions of users’ accounts. The US will vigorously investigate and prosecute the people behind such attacks to the fullest extent of the law."