ALEXANDRIA, Va., Aug. 6 (UPI) -- A cyberattack launched from Russia last month successfully hacked into a non-classified Pentagon email system used by personnel of the Joint Chiefs of Staff, U.S. officials said Thursday.
The officials told NBC News the breach was sophisticated and managed to gather large amounts of data and disseminate it to various accounts on the Internet.
Encrypted social media accounts were also used to coordinate the attack, officials said.
The sources emphasized, though, the information exposed by the breach was not classified. Also, it isn't known for certain whether the attack was state-sponsored -- but the Pentagon reportedly believes the scope of the attack suggests it likely was.
"It was clearly the work of a state actor," an official told NBC News.
The hack occurred sometime around July 25 and affected about 4,000 military and civilian employees of the Joint Chiefs of Staff. In response the Pentagon immediately shut down the email system, which is still offline. It was expected to resume functions perhaps as soon as Thursday.
If the breach was conducted by Russian government officials, the Pentagon believes it wasn't the first time. Moscow is believed to have been behind another hack of White House and State Department computers in October.