Russians are responsible for infiltrating the State Department and White House computer systems in recent months, CNN reported Tuesday.
The report says the hackers had access to non-classified, sensitive information, such as the president's schedule, by first breaking into the State Department.
The Obama administration had acknowledged suspicious activity in the unclassified network that serves the executive office of the president in October, but had not said who was behind it.
On Tuesday, the White House again declined to comment on who is responsible.
“This report is not referring to a new incident – it is speculating on the attribution of the activity of concern on the unclassified EOP network that the White House disclosed last year,” National Security Council Spokesperson Mark Stroh said. “Any such activity is something we take very seriously. In this case, as we made clear at the time, we took immediate measures to evaluate and mitigate the activity.”