A group of hackers has attacked the Office of Personnel Management (OPM), stealing sensitive data on 4 million current and former American federal employees. Law enforcement sources tell Reuters that the government believes the perpetrators are from China and have penetrated not just OPM's IT systems, but also the records it stores at the Department of the Interior's data center. According to the New York Times, security researchers believe it's the same crew that attacked insurance companies Anthem and Primera. As you might know, OPM is in possession of a huge number of personnel info since it's in charge of conducting background checks on potential federal employees. It probably looks like a goldmine for data thieves and was even targeted last year (nothing was stolen at that time, though) by a group, which the government suspects is also based in China.