“Hackers working for the Chinese state breached the computer system of the Office of Personnel Management in December…and the agency will notify about 4 million current and former federal employees that their personal data may have been compromised,” The Washington Post reports.  

“The hack was the largest breach of federal employee data in recent years. It was the second major intrusion of the same agency by China in less than a year and the second significant foreign breach into U.S. government networks in recent months… The intruders in the OPM case gained access to information that included employees’ Social Security numbers, job assignments, performance ratings and training information.”  

“The intruders used a ‘zero-day’ — a previously unknown cyber-tool — to take advantage of a vulnerability that allowed the intruders to gain access into the system.”