2015 Office of Personnel Management data breach

The Office of Personnel Management data breach was a 2015 data breach targeting Standard Form 86 (SF-86) U.S. government security clearance records retained by the United States Office of Personnel Management (OPM). One of the largest breaches of government data in U.S. history, the attack was carried out by an advanced persistent threat based in China, widely believed to be the Jiangsu State Security Department, a subsidiary of the Government of China's Ministry of State Security spy agency.

Source: Wikipedia — 2015 Office of Personnel Management data breach (CC BY-SA 4.0)