Russian hackers suspected in cyber-attack on General Dempsey’s office

The office of the U.S. Joint Chiefs of Staff, has been hit by hackers. It appears the Russians are to blame for the sophisticated cyber-attack on the unclassified e-mail network of the military command.

U.S. officials said the attack last month affected nearly 3,000 civilian and military personnel, working for the Joint Chiefs of Staff, and the network was shut down for two weeks.

According to investigators, the hack was a “spearphishing” attack, which involves scammers sending e-mails that appear to be from colleagues. “The latest set of attacks used hundreds of e-mails with a zipfile attachment that, if double-clicked, could introduce malware to an organization’s networks,” they said.

Officials told Reuters the attack “bore the hallmarks of a foreign state, as opposed to a less sophisticated hacker.” The hackers used an automated system that rapidly gathered massive amounts of data.

The Telegraph reported that the hackers used encrypted social media accounts to launch the attack. No classified information was obtained, the report said, but the Pentagon decided to shut the email system down pending the investigation.

The rest of the Pentagon was reportedly unaffected in this latest attack. But in April, Defense Secretary Ash Carter blamed Russian hackers for a cyber-intrusion on an unclassified U.S. military network, saying they discovered an “old vulnerability that had not been patched.”

Cybersecurity experts say they’ve seen a “massive escalation” in cyber-attacks tied to the Russian government since sanctions were imposed last year over Moscow’s aggressive actions in Ukraine.