Hackers based in China breached U.S. Office of Personnel Management computers, according to American officials, stealing records of as many as 4 million current and former federal employees in one of the largest breaches of government personnel data.
The hackers, believed to have links to the Chinese government, got into the computer system late last year, according to one U.S. official, who asked for anonymity to discuss the investigation. The intrusion was detected in April and it took U.S. investigators a month to conclude that the files had been compromised.