(VOVworld) - The Pentagon took its Joint Staff unclassified email system offline nearly two weeks ago, after detecting a "sophisticated cyber attack" by alleged Russian hackers. The US media said on Friday that the intrusion occurred sometime around July 25^th and affected about 4,000 military and civilian personnel who work for the Joint Chiefs of Staff. It added the suspected Russian hackers, called APT29, coordinated the attack via social media accounts. Almost immediately after the cyber attack was detected the Pentagon shut down the entire Joint Staff unclassified email system. The system is expected to be back online before the end of this week.