The U.S. State Department shut down some unclassified email systems after hackers staged an attack in recent weeks. 

A U.S. official, who requested to keep his identity confidential, told the Associated Press that the systems were not compromised; they were shut down to ensure security after some unauthorized activity was detected in late October.

Prior to the State Department attack, the hackers initially targeted the White House computer network, which was reported in October. Since then, other agencies fell victim, including the U.S. Postal Service and the National Weather Service. The U.S. Military confirmed that its systems were secured.

"The department is implementing improvements to the security of its main unclassified network during a scheduled outage of some Internet-linked systems," the official said.

The State Department is expected to be back online soon and might address it by Monday or Tuesday.

The lawmakers have requested the State to provide more information about the attack by Jan. 5 for documentation, and for them to draft new policies to better protect consumer and government data.

Temporarily, some U.S. officials were asked to stop using their official emails and use Gmail instead, the Telegraph reported. There are assumptions that it could either be Russia or China as the ones responsible for initiating the privacy breaches, but the FBI is still investigating.

"We are aware of these reports and are working with our interagency partners to investigate the matter," FBI spokesman Joshua Campbell said in an email to Businessweek.

"The compromise of public and private sector systems is something we take very seriously, and the FBI will continue to investigate and hold accountable those who pose a threat in cyberspace," he added.