In an internal memo, Pentagon leadership has urged military personnel not to take mail-in DNA tests, warning that they create security risks, are unreliable and could negatively affect service members’ careers.

The letter, which was reported by Yahoo News, was sent last week. It does not name any particular DNA testing companies, but counsels broadly against buying ancestry and health tests promoted with military discounts and other military incentives.

Cmdr. Sean Robertson, a Pentagon spokesman, confirmed that the memo had been sent.

“We want to ensure all service members are aware of the risks of Direct to Consumer (DTC) genetic testing,” he told The New York Times over email.

Over the past decade, millions of Americans have purchased DNA tests through companies such as 23andMe and Ancestry with the hopes of connecting with relatives, finding out more about their family origins and learning about how their DNA could affect their chances of developing certain health conditions.

Robertson said that the tests might provide inaccurate results and have negative professional consequences. “The unintentional discovery of markers that may affect readiness could affect a service member’s career,” he said.

The Genetic Information Nondiscrimination Act — known as GINA — prohibits discrimination by health insurers and employers based on the information that people carry in their genes. It does not apply to members of the military, however.

The memo was written by Joseph Kernan, the undersecretary of defense for intelligence, and James Stewart, the assistant secretary of defense for manpower. They warn that the tests “could expose personal and genetic information, and potentially create unintended security consequences.”

In a statement, a spokeswoman from 23andMe said that the company took great care to protect customers’ privacy. An Ancestry spokeswoman said that the company had not targeted military personnel with discounts.