The US State Department has shut down its unclassified email system as it evaluates potential damage caused by a possible hacker attack.
The department's email system was shut down in a planned outage Friday to make repairs and security upgrades after "activity of concern" was detected recently on the system, according to the Associated Press. None of the department's classified email system was affected by the suspected breach, according to a senior department official who spoke to the news agency on condition of anonymity.
"The department recently detected activity of concern in portions of its unclassified e-mail system," a senior State department official told CNET. "There was no compromise of any of the Department's classified systems."
The State Department said it expects to have email access restored soon. The department is expected to address the outage Monday or Tuesday, according to the AP.
It was not immediately clear who might be behind the department's suspected hack, the fourth incident in recent months in which a government agency has been targeted by an apparent hack attack. After a security breach of an unclassified network used by White House advisers was revealed last month, suspicion immediately fell on hackers thought to be working for the Russian government.
The National Oceanic and Atmospheric Administration, which includes the National Weather Service, revealed last week that four of its websites were compromised in recent weeks by an "Internet-sourced attack." Chinese government hackers were suspected in that attack, as well as one on the US Postal Service, in which data for more than 800,000 employees was compromised.
Updated November 17 at 9:30 a.m. PT with State Department comment.