The US Department of State took its unclassified email system offline at the end of last week, in a bid to repair damage caused by a hack in late October.
Suspicious activity took place on the department’s network at the same time that the White House’s infrastructure was attacked, with part of the department’s public website also knocked out.
A spokesman for the Department of State, which is responsible for American foreign affairs, said no classified systems were affected by the maintenance, expected to finish today or tomorrow.
He refused to discuss who was responsible for the breach, the sort of attack often attributed to US rivals China or Russia by security researchers, but further details are expected to be released this week once the service is restored.
The shutdown follows similar attacks on the country’s National Oceanic and Atmospheric Administration (NOAA) and Postal Service last week.
While the attack on the weather service forced a shut down for unscheduled maintenance, the postal service breach potentially compromised personal data of 800,000 workers, as well as some customers.
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