Russian-hired hackers breached an unclassified White House system and pilfered information about President Obama's daily schedule and communications, CNN reports.

The hackers gained "access to sensitive information such as real-time non-public details of the president's schedule."

A phishing-style attack allowed Russian hackers to access a State Department computer network, which in turn allowed access to the White House's system.

The hackers were working for the Russian government but did not succeed in accessing any classified networks, according to CNN.

Even so, nonclassified networks can contain sensitive information that the White House might not want in the hands of a rival government. And it is a sign that even high-level US government systems are far from impervious to outside attacks. The Air Force Space Command Network Operations & Security Center at Peterson Air Force Base in Colorado Springs, Colorado. REUTERS/Rick Wilking The attack stemmed from a nearly yearlong breach of the US State Department's computer systems that investigators described as the "worst ever" against a US federal agency target, according to a CNN report in March. Those ongoing problems with the computer networks have apparently now affected the White House as well.

On CNN, White House deputy national security adviser Ben Rhodes explained that federal staffers had been encouraged to guard even nonclassified information being passed through government systems because of hacking concerns. US deputy national security adviser Ben Rhodes. Kevin Lamarque/Reuters "If you're going to do something that is classified, you have to do it on one email system and on phone system, and act as if information could be compromised if it's not on the classified system," he said. Rhodes said the hackers did not access classified information, even though the government views unclassified information as "sensitive."

Rhodes would not comment on whether Russian hackers were responsible for the reported White House breach.

"It's fair to say ... Russia has been active in the cyberspace and in the espionage space," Rhodes told CNN.