Russian hackers broke into the White House computer system and obtained sensitive information, including details of US President Barack Obama’s timetable, CNN reported on Wednesday.
Details about the security penetration were revealed by unnamed US officials who were briefed about the investigation into the attack, the report said.
In an initial response the White House admitted the breach, but noted that the information the hackers were able to access was all unclassified, albeit not for public consumption.
National Security Council spokesman Mark Stroh would not confirm if the Russians were behind the attack and said only that “any such activity is something we take very seriously.”
There was no comment from the State Department or the Russian Embassy, CNN said.
The hackers’ activity first came to the attention of White House security officials last October when they noticed peculiar behavior in the unclassified computer network of the president’s executive office, which had been undergoing security upgrades.
After officials became aware of the intrusive behavior, the FBI, Secret Service, and intelligence agencies were all called in to handle the investigation.
According to the report, the hacking method was very sophisticated and employed computer routers all over the world in an attempt to disguise the origin of the attack. However, investigators identified snippets of code that pointed to hackers working for the Russian government.
Obama’s deputy national security adviser, Ben Rhodes, said classified information is stored on a separate system to protect top-secret material from hacking attempts.
“We do not believe that our classified systems were compromised,” Rhodes told CNN.
“In this case, as we made clear at the time, we took immediate measures to evaluate and mitigate the activity,” he said. “As has been our position, we are not going to comment on [this] article’s attribution to specific actors.”
The hackers used a phishing email — a fake email message used to surreptitiously gather information — to penetrate the American government network via the State Department and from there attacked the White House.
Russian hackers have made repeated attacks on the State Department computer system for the past few months, the report said.
Director of National Intelligence James Clapper told a Senate hearing in February that the “Russian cyber-threat is more severe than we have previously assessed.”
The White House hacking attack came after revelations last month that possible US presidential candidate Hillary Rodham Clinton used a private email account to send official business messages during her time as secretary of state in 2009-2013.
Clinton’s extensive use of private emails raised questions in the buildup to her expected presidential run about whether she adhered to the letter or spirit of accountability laws.
A State Department official, speaking on condition of anonymity, said at the time the department would review 55,000 pages of emails amassed from Clinton’s personal files to determine if there were any instances where she improperly transmitted sensitive information.
Clinton aides and the State Department both say she never received or transmitted classified information on her private email account. But unclassified diplomatic details and internal matters are sometimes considered sensitive and can be targeted by hackers and foreign governments.
Associated Press contributed to this report.