Russian Hackers Suspected in Cyberattack on Pentagon Emails of 4K Joint Chiefs of Staff employees affected By Michael Harthorne, Newser Staff Posted Aug 6, 2015 6:47 PM CDT 22 comments Comments (Shutterstock) (Newser) – Officials believe Russian hackers are behind a cyberattack on the Pentagon's unclassified email system that has left approximately 4,000 employees of the Joint Chiefs of Staff without email for nearly two weeks, NBC News reports. The attack happened sometime in the last week of July, and while officials say no classified information was seized or compromised, the Pentagon was forced to shut down the entire Joint Chief email system. According to the Daily Beast, one defense official called it the "most sophisticated" attack yet on the network. The cyberattack was coordinated through social media, according to NBC News. And the Daily Beast reports it was carried out by sending emails that appeared to be legitimate but actually contained malware. Investigators believe the Russian hackers behind the attack are the same people behind similar attacks on the White House and State Department last year. NBC says it's unclear if the attack was backed by the Russian government, but CNBC cites one official who says the attack was "clearly the work of a state actor" based on its scope.