U.S. officials said that last year, Russian hackers were able to get into the White House's non-public, non-classified computer system for several months.
The hackers were difficult to detect and to remove from the network, a source told ABC News, and the White House had to shut the system down for several days. The network is used by the White House advance and press office, officials in the budget and legislative liaison offices, and the general counsel's office, and some believe that the hackers might still have access, the source said.
The White House National Security Council said in a statement it disclosed the hacking last year and "any such activity is something we take very seriously."