In June 2015, the United States Office of Personnel Management (OPM) announced that it had been the target of a data breach targeting personnel records. Approximately 22.1 million records were affected, including records related to government employees, other people who had undergone background checks, and their friends and family. One of the largest breaches of government data in U.S. history, information that was obtained and exfiltrated in the breach included personally identifiable information such as Social Security numbers, as well as names, dates and places of birth, and addresses. State-sponsored hackers working on behalf of the Chinese government carried out the attack.

https://en.wikipedia.org/wiki/Office_of_Personnel_Management_data_breach