Human rights advocates are worried that a biometric system containing the personal information of millions of Afghans could fall into the hands of the Taliban, NBC News reported Tuesday.

The system could enable the Taliban to identify and seek retribution against people who worked with the U.S.-backed Afghan government or international organizations that promoted women’s rights, said NBC News, which spoke with three military veterans who worked on the biometrics project.

Created by the U.S. more than 15 years ago, the system contains millions of fingerprints, iris scans, and face photos of Afghan people who had their biometric data collected by U.S. and coalition forces.

The system, which was shared in part with the Afghan government, originally was meant to help track global terrorists.

A group of 36 civil society organizations last week signed a joint letter calling on governments, aid organizations, and private contractors that created databases in Afghanistan to take immediate action to shut them down and erase them, NBC News said.

“Under authoritarian regimes, these [biometric] data have been used to target vulnerable people, and digitized, searchable databases amplify the risks of abuse of this data,” the letter read.

A Department of Defense spokesman told NBC News the biometric data was not at risk.

“The U.S. has taken prudent actions to ensure that sensitive data does not fall into the Taliban’s hands. This data is not at risk of misuse,” spokesman Eric Pahon said.

Two U.S. military veterans who worked on the program, however, told NBC News there’s a particular fear that any biometric data list could be used to target women.

Although the Taliban recently promised to protect the rights of women, there have been reports of female activists being beaten. The United Nations said the number of women and children killed this year had reached its highest levels since the U.N. began keeping records in 2009.

“A lot of people are concerned that if there is some way for the Taliban to use the biometrics information, that it could be used to target women who worked in any sort of government position, women police or women journalists,” one military officer told NBC News.

The Defense Department would not say how many Afghans are in the system, though it is believed to be extensive. A former Air Force medic told NBC News he had been ordered to scan the irises, take the fingerprints, and photograph the faces of every Afghan who came through the hospital in which he worked.

“Men, women, children, dead children, dead bodies, every person I encountered would be put into the biometrics system,” the medic told NBC News.

One Afghanistan War veteran told NBC News the information would be of little use to people without knowledge of how to narrow the datasets.

“Whether you’re in a database or not doesn’t confirm or deny that you have any sort of U.S. allegiance,” the veteran told NBC News. “At its core level, it’s a positive ID. You’re confirming you are who you say you are.”