In April of 2015, IT staffers within the United States Office of Personnel Management (OPM), the agency that manages the government's civilian workforce, discovered that some of its personnel files had been hacked. Among the sensitive data that was exfiltrated were millions of SF-86 forms, which contain extremely personal information gathered in background checks for people seeking government security clearances, along with records of millions of people's fingerprints.
The OPM breach led to a Congressional investigation and the resignation of top OPM executives, and its full implications—for national security, and for the privacy of those whose records were stolen—are still not entirely clear. As the official Congressional report on the incident says, "The exact details of how and when the attackers gained entry ... are not exactly clear." Nevertheless, researchers have been able to construct a rough timeline of when the breaches began and what the attackers did.

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