Chinese hackers attack computer systems of White House, US presidential candidates

According to the government official, the National Cyber Investigative Joint Task Force had discovered the "intrusion," which was most likely "state-sponsored," on the White House's unclassified computer network and had traced back the attacks to servers based in China.

"We are getting very targeted Chinese attacks so it stretches credulity that these are not directed by government-related organizations," the official said.

The official said that the hackers managed to penetrate the White House system for brief periods that allowed them to steal information before US government experts patched the system.

"For a short period of time, they successfully breach a wall, and then you rebuild the wall...it is not as if they have continued access. It is constant cat and mouse on this stuff," he said.

The more secure classified network has not been breached, he added.