Russian hackers who hit the White House infiltrated an unclassified computer system and apparently accessed details about President Obama's schedule.
While the White House previously sought to downplay the seriousness of the hack, which took place last year, the intruders were able to see information about the president that was not publicly available, CNN reported Tuesday.
Officials briefed on the investigation told CNN that the incident was connected to a Russian cyberattack that also breached the State Department's network.
While a general outline of the day’s events is available to the press, Obama takes many meetings and phone calls throughout the day that are not publicly disclosed.
The president’s precise whereabouts are also not always known, and the press pool that covers Obama on a daily basis is restricted from accessing many parts of the White House building and grounds.
Intimate knowledge of Obama’s activities would be seen as valuable to foreign intelligence agencies like Russia’s.
Officials with knowledge of the investigation told CNN that Russian hackers were able to break into the White House system through their foothold within networks at the State Department.
The intrusion began when hackers sent what is known as a "phishing" email from a State Department account, infecting a White House computer with malware, the investigators said.
The State Department has been battling its own highly sophisticated cyber intrusion for months, though exactly which portions of its network remain breached is unclear.
Private security experts had suspected there was a link between the State Department and White House break-ins.
Russia is a key adversary of the United States in cyberspace, and is believed to have infiltrated most U.S. critical infrastructure, including installing malware in software that controls everything from oil and gas pipelines to wind turbines to nuclear power plants.
The White House breach made headlines last year as a sign of hackers’ increasing access to the highest levels of the U.S. government.
White House officials confirmed in October that its unclassified system had been breached. Computers and systems were not damaged, officials said, though some services were disrupted as cybersecurity experts sought to limit hackers’ activity in the months that followed.
The “vast majority” of systems were back online as of late February, White House press secretary Josh Earnest said at the time.
—Last updated at 6 p.m.