The number of people whose fingerprints have been stolen as a result of the high-profile hack into the computer systems of the U.S. Office of Personnel Management earlier this year is now 5.6 million.
The agency revised its original estimate of 1.1 million Wednesday after finding fingerprint data in archived records that had previously not been taken into account.
This does not change the overall number of 21.5 million former, current, and prospective federal employees and contractors whose Social Security numbers, personal information, and background investigation records were exposed in the breach.
The OPM announced in June that it was the target of a cyber security breach that resulted in the theft of personnel data including full names, birth dates, home addresses, and Social Security numbers of 4.2 million current and former government employees.
A subsequent investigation revealed that sensitive data on 21.5 million people who underwent background checks, including federal employees or contractors and their spouses or cohabitants, had also been compromised.
Around 5.6 million of those records are now known to have also included fingerprints.
A working group of experts from the FBI, DHS, DOD, and the intelligence community are working to understand the potential ways in which attackers could use the fingerprint data.
For now, federal experts believe that the possibility of misuse is limited, but they're working to develop defenses against potential abuse, the agency said. "If, in the future, new means are developed to misuse the fingerprint data, the government will provide additional information to individuals whose fingerprints may have been stolen in this breach."
All affected individuals and their minor dependent children are eligible for free identity theft and fraud protection services.
Bloomberg reported in July, citing anonymous sources, that a hacker group from China was responsible for the security breaches at both OPM and health insurer Anthem. According to security firm Symantec, the group that breached Anthem has access to an attack platform called the Elderwood framework that is shared by multiple cyber espionage groups based in China.
Some security experts believe that the data stolen from OPM is a counterintelligence gold mine that could allow a foreign intelligence agency to unmask undercover U.S. agents, identify people with security clearances to target, or to use potentially embarrassing information against employees to turn them into informants.