A cyber attack has been detected on the unidentified e-mail network of the U.S Joint Chief of Staff, which reportedly forced the military command to shut the system off on Thursday, August 6. According to reports, Russia is the main suspect in this currently unresolved case.

U.S officials said in a statement, that the hack was a 'spear phishing attack' where scammers would send the e-mails that allegedly are from a sender's colleagues.

They added that if it happens that the e-mail attachments are accidentally double-clicked, the files would introduce malware to get into the system. The officials also said that the unidentified hackers have used an automated system, which made their hacking faster than the usual.

Despite the alarming reports, the officials confirmed that there has been no classified information that was taken hold of or compromised.

The Pentagon also confirmed the unidentified e-mail system of the U.S Joint Staff, which occupies about 2,500 civilians and personnel, was taken offline over the weekend. The rest of the Pentagon appeared unaffected.

Though one of the U.S officials has spoken on the anonymity of the real suspect and Russia being initially blamed, they had also put an emphasis that more time would be needed for the investigators to trace the people responsible for the incident.

"We continue to identify and mitigate cyber security risks across our networks," Lieutenant Colonel Valerie Henderson, a spokeswoman from the Pentagon said in her statement. "With those goals in mind, we have taken the Joint Staff network down and continue to investigate. Our top priority is to restore services as quickly as possible."

Prior to the hacking, U.S Defense Secretary Ash Carter first blamed the Russian hackers for a cyber intrusion which occurred in late April, where the U.S military network discovered an old vulnerability that had not been fixed.

Dmitei Alperovitch, a chief technology officer and co-founder of Crowdstrike, a well-known cyber-security firm, said that his team discovered a "massive escalation" in the cyber attacks connected to the Russian government.

Though he said that no information was gathered on the cyber attack, he revealed that his company was able to detect a few more suspected hacks from US national security agencies and commercial firms by a known hacker group called 'Cozy Bear'.

The group of hackers has been engaged in different cyber attacks which range from spear phishing to a more sophisticated method that can be very difficult to resolve. Alperovitch said, "Once they get a beachhead, their trade craft is very, very good."