White House confirms cyber-attack on 'unclassified' system

The White House has confirmed it was the target of a cyber-attack but says the breach hit an unclassified network.

An unnamed administration official told US media that there was no indication any data had been removed.

The conservative Washington Free Beacon reported on Sunday that hackers linked to the Chinese government had breached the White House Military Office.

The White House would not say if the attack originated in China, describing it as a "spear-phishing" attempt.

"Spear-phishing" typically works by sending fake e-mails that look like legitimate correspondence, but which link to a malicious website or file attachment.

"These types of attacks are not infrequent and we have mitigation measures in place," the official, who was not authorised to speak on the record, told the Associated Press and other US media.

Cyber-attacks from Chinese-linked hackers have been an increasing concern among US government offices, including the Pentagon, the head of intelligence for US cyber defence told Reuters last week.

"Their level of effort against the Department of Defense is constant," Rear Admiral Samuel Cox said.

In 2011, Google blamed computer hackers in China for a phishing effort against Gmail accounts of several hundred people, including senior US government officials and military personnel.

That November, senior US intelligence officials for the first time publicly accused China of systematically stealing American high-tech data for its own gain.