Chinese hackers broke into the computer networks of the United States government agency that keeps the personal information of all federal employees in March, the New York Times reported, citing senior US officials.
The hackers appeared to be targeting files on tens of thousands of employees who have applied for top-secret security clearances, the newspaper said.
The hackers gained access to some of the databases of the Office of Personnel Management before federal authorities detected the threat and blocked them from the network, the newspaper said.
It was not yet clear how far the hackers penetrated the agency's systems, in which applicants for security clearances list their foreign contacts, previous jobs and personal information like past drug use.
Tensions are high between China and the United States.
The United States recently charged five Chinese military officers, accusing them of hacking into American companies to steal trade secrets. China showed its anger over the allegations by shutting down a bilateral working group on cyber security.
On Wednesday, China and the United States began annual talks in Beijing, called the Strategic and Economic Dialogue, expected to focus on cyber-security, maritime disputes, the Chinese currency and an investment treaty.