The unprecedented shutdown on Friday was reportedly applied to give technicians an opportunity to repair possible damage, as well as to apply security improvements. A senior department official said possible problems were detected at around the same time as a previously reported attack on the White House computer network in late October.
However, access to public websites from the State Department's main unclassified system have been affected. The official US State Department website is up and running.
The extent of the possible breach, much yet who might be behind it, remains unclear from early reports (CNN, NY Times, following up on an initial report by AP). The State Department reportedly expects to have the system back up and running by either Monday or Tuesday.
In the two weeks or so since the White House attack became public other US government agencies, including the US Postal Service and the National Weather Service, have reported attacks.
Russian hackers are the main suspects in the White House breach while the breaches at NOAA and the Postal Service are thought by some to be the work of Chinese hackers. Security watchers suspect the hidden hand of nation states is behind the run of attacks on US government systems.
"To me this looks like hacking groups - either independent or state sponsored - in reconnaissance phase, probing government agency networks to identify vulnerabilities and what data they can access," Ken Westin, a security researcher at security tools firm Tripwire writes. "Although no damage has been inflicted on these systems, the outages do have an impact and could be a precursor to a more organised attack."