WASHINGTON - The White House acknowledged Monday that one of its computer networks was hit by a cyber attack, but said there was no breach of any classified systems and no indication any data was lost.

An administration official made the comment after a report from a right-wing news site that Chinese hackers had breached a key White House military system.

The US official said the attack was against "an unclassified network" and was a case of "spear phishing," in which a spoofed email tricks a user into clicking through to a website where a hacker can install malicious software or gain control of another computer.

"These types of attacks are not infrequent and we have mitigation measures in place," the official said.

"In this instance, the attack was identified, the system was isolated, and there is no indication whatsoever that any exfiltration of data took place. Moreover, there was never any impact or attempted breach of any classified system."

On Sunday, a report by the Washington Free Beacon -- a website operated by a group claiming to report news ignored by "the professional left" -- said hackers linked to China's government breached a system used by the White House military office for nuclear commands.