U.S. officials believe Russian hackers that broke into the State Department used their access to break into White House computers containing sensitive information, including details on the president's whereabouts, CNN reported.
Hackers hired by Russia have long been suspected of a security breach at the State Department in recent years, despite repeated efforts to expel them from the system, investigators told CNN.
From there, the suspects hacked into computers in the president's executive office by sending an email from a compromised State Department account pretending to be an official seeking access, or what National Intelligence Director James Clapper called "phishing."
"So many times, the Chinese and others get access to our systems just by pretending to be someone else and then asking for access, and someone gives it to them," Clapper said at an FBI cyberconference in January, CNN reported.
Investigators said the White House hack, noticed last October, targeted a system that was unclassified. But the information breached was still of a sensitive nature and highly sought after by foreign intelligence agencies, including details on the president's schedule not made available to the public.
While federal investigators would not confirm if the hack was Russian, there were signs found in codes that pointed a finger towards Moscow. The National Security Council said the White House breach was eliminated.
"In this case, as we made clear at the time, we took immediate measures to evaluate and mitigate the activity," spokesman Mark Stroh told CNN. "As has been our position, we are not going to comment" on the assertion that Russia is involved.
The Russian hack, if true, comes at a time of tension between the U.S. and the eastern European country over its suspected involvement in the Ukrainian crisis.
As the investigation continues, President Barack Obama's staff said the White House's classified systems were not compromised. Officials are told to prepare for a possible hack by keeping every classified detail on one single system.
"In other words, if you're going to do something classified, you have to do it on one email system, one phone system," Ben Rhodes, Obama's deputy national security advisor, told CNN. "Frankly, you have to act as if information could be compromised if it's not on the classified system."