Russian hackers who compromised computers in the US State Department used the foothold to target the White House computer system, it is claimed.
Computer experts allegedly backed by the Russian government penetrated sensitive parts of the White House computer system, CNN and other US news networks cited senior officials as saying.
Information access reportedly included real-time non-public details of the president's schedule. The information is not classified but still highly sensitive.
The hackers routed their attacks through computers around the world to hide their origins, but investigators say tell-tale codes point to hackers working for the Russian government.
National Security Council spokesman Mark Stroh would not confirm the exact details of the case, but said "any such activity is something we take very seriously".
It is alleged that suspicious activity was noticed on the White House computer systems back in October.
One official was quoted by CNN as saying the Russian hackers have "owned" the State Department system for months despite efforts to lock them out.
The Obama administration admitted the State Department computer intrusion when it happened last year, but said it would not comment in detail on the new claims.
Last week Mr Obama signed an executive order approving the first sanctions programme against cyberattackers who pose a "significant threat" to American interests.