* Federal personnel office hacked for second time in a year
* Cybersecurity expert sees "huge uptick" in data theft
* Defense chiefs worry over copycat weapons systems (Adds details on link to Chinese intelligence)
By Andrea Shalal
WASHINGTON, June 6 (Reuters) - A massive breach of U.S. federal computer networks disclosed this week is the latest in a flood of attacks by suspected Chinese hackers aimed at grabbing personal data, industrial secrets and weapons plans from government and private computers.
The Obama administration on Thursday disclosed the breach of computer systems at the Office of Personnel Management and said the records of up to 4 million current and former federal employees may have been compromised.
U.S. officials have said on condition of anonymity they believe the hackers are based in China, but Washington has not publicly blamed Beijing at a time when tensions are high over Chinese territorial claims in the South China Sea.
China has denied involvement.
It was the second computer break-in in less than a year at the OPM, the federal government's personnel office.
The first breach has been linked to earlier thefts of personal data from millions of records at Anthem Inc, the second largest U.S. health insurer, an attack also blamed on Chinese hackers, and Premera Blue Cross, a healthcare services provider.
Guidance Software, a cybersecurity firm, said the first signs of data "exfiltration" were originally detected with Einstein, a U.S. government intrusion detection system. That activity, it said, was eventually traced back to a machine under the control of Chinese intelligence.
"It's a different form of Cold War at this point," said Rob Eggebrecht, co-founder and chief executive of Denver-based InteliSecure, a private cybersecurity firm.
Eggebrecht said his firm had seen a spike in attacks on private company networks by Chinese actors over the past three months. The latest was a previously undisclosed breach at a U.S. pharmaceutical group, which cost the firm hundreds of millions of dollars in sensitive research and development work.
Eggebrecht declined to identify the firm, which he said only learned of the major breach within the last 72 hours.
"We've seen a huge uptick in opportunistic exfiltration of high-value data," he said, adding that the attack on the pharma company involved malicious software installed together with the Chinese-language search engine Baidu.
"DIZZYING RATE"
Admiral James Winnefeld, vice chairman of the Joint Chiefs of Staff, told a cyber conference at West Point military academy last month that U.S. adversaries like China and Russia were rapidly increasing their assaults on military networks.