WASHINGTON (AP) — Chinese hackers broke into the computer networks of the Office of Personnel Management earlier this year with the intention of accessing the files of tens of thousands of federal employees who had applied for top-secret security clearances, according to The New York Times.

Senior U.S. officials say the hackers gained access to some of the agency’s databases in March before the threat was detected and blocked, the Times reported in an article posted on its website Wednesday night. How far the hackers penetrated the agency’s systems was not yet clear, the newspaper said.