WASHINGTON (AFP) - Hackers based in Russia penetrated the email network of the Pentagon's Joint Chiefs of Staff, leading to a two-week shutdown of the system, NBC News reported Thursday.
The Pentagon confirmed that the Joint Chiefs' email system was taken offline pending an investigation but declined to elaborate.
"We continue to identify and mitigate cybersecurity risks across our networks," Pentagon spokeswoman Lieutenant-Colonel Valerie Henderson said.
"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.
"As a matter of policy and for operational security reasons, we do not comment on the details of cyber incidents or attacks against our networks."
NBC, citing unnamed sources, said it was not clear if the attack had been sanctioned by the Russian government.
But the sources told the network that the cyberattack relied on an automated system that rapidly gathered massive amounts of data.
According to officials who declined to be identified, the intrusion occurred around July 25 and affected some 4,000 military and civilian personnel, NBC said.
The officials said no classified information was seized or compromised but that the Pentagon decided to shut down the entire email system during its investigation.
The news comes after US officials confirmed some 21 million US government employees, contractors and others had personal information compromised in two breaches.
Officials have declined to identify the source of the hack of personnel records but it is widely believed to be part of a Chinese espionage program.