WASHINGTON, June 7 (UPI) -- Rep. Michael McCaul, R-Texas, chairman of the Homeland Security Committee, said on Sunday he believes "China was responsible" for hack on federal employees earlier this year.
The personal data of an estimated 4 million current and former federal employees was compromised in the computer breach, which some security experts believe could be the beginning of future attacks.
"I believe, in my judgment, that all threat indicators point to China," McCaul told host John Dickerson on CBS's Face the Nation. "In my judgment, China was responsible for this."
The U.S. Office of Personnel Management, which handles government security clearances and federal employee records, said it became aware of the data breach in April. Personally identifiable information, including social security numbers, was potentially illegally accessed, the White House announced on Thursday.
"This is the most significant data breach in U.S. history," McCaul added. "It was perhaps nation-state sponsored because of the way it was done. It was done for espionage."
The hack could have been carried out by the same Chinese hackers who breached the database of Anthem Insurance, when hackers exposed about 80 million Social Security numbers.
Several cybersecurity experts who are advising the government told CNN the hack could be part of a Chinese plan to build a vast database in what may be preparation for future attacks against the United States.
The hackers may use the personal information to impersonate government workers to set up for future "insider" attacks. China may identify, expose and blackmail U.S. government officials around the world if it reveals security clearance details, according to the experts.
Danielle Haynes contributed to this report.