The Navy's top officer warned against using popular at-home ancestry DNA test kits this week, saying scientific advancements are making biological weapons more tailorable.

Biological weapons that can target specific groups or individuals vulnerable to pathogens or other diseases are a growing national security concern, Chief of Naval Operations Adm. John Richardson said during a Tuesday speech on nuclear deterrence in Washington, D.C.

"Be careful who you send your DNA to," Richardson said at the event, hosted by the Mitchell Institute for Aerospace Studies. "There's a number of those companies where you can go and find out what your makeup is. That's a lot of information.

"You learn a lot about yourself, and so does the company who's doing it," the CNO added.

More than 26 million people have taken at-home ancestry tests, according to a study from the Massachusetts Institute of Technology. Based on the rate at which people are buying the kits, that number could jump to 100 million by 2021, the study adds.

Officials with AncestryDNA, one of the leading companies that offer mail-in tests, says protecting customers' privacy and data remains the company's highest priority.

"Customer DNA data in Ancestry's systems is de-identified, encrypted and segmented to a separate, dedicated access-controlled storage platform," Jasmin Jimenez, an Ancestry.com spokeswoman, said. "Our customers maintain ownership and control over their own data at all times."

The company doesn't share customer DNA with insurers, employers or third-party marketers, she said. And personal data, she added, is only provided to law enforcement officials if there is a valid legal process, such as a court order.

A spokesman for 23andMe, another popular genetic test site, cited similar privacy safety protocols, with multi-layer encryption of customer data and restricted access to the company's systems.

Paul Rosenzweig, a cybersecurity expert with R Street Institute who served as President George W. Bush's Department of Homeland Security deputy assistant secretary for policy, said people must treat their DNA like any other personal data.

"Share it sparingly and only with people you trust, because it can be misused by malicious actors," he said.

Steven Block, a biology and applied physics professor at Stanford University, agrees that people should be mindful of database hacking threats. But they tend only to store a limited amount of data, he added, since people share just a subset of their genetic info -- about 1/1,000th of their full DNA -- when taking most ancestry tests.

"If you have the physical swab, then you have a sample of the complete DNA information for the individual, and the potential to do much more with that than, say, the sort of limited information that ancestry-kit companies collect and store," Block said.

Unless someone carries a rare mutation, it's unlikely that information from a DNA test would be used to personalize a bioweapon, he added, since it would require so much work to develop and test it.

"All that requires special expertise and resources," Block said. "This is not the sort of thing someone might cobble together readily in a garage -- at least not any time soon. ... Also, you have to ask whether a personalized bioweapon is really the most practical way to assassinate someone."

That's not to say bad actors have never relied on action-movie-style assassination techniques. Block referenced the 2017 assassination of Kim Jong Nam using a nerve agent-soaked cloth; the 2006 case in which former Russian agent Alexander Litvinenko drank poison-laced tea; and the 1978 murder of Bulgarian dissident and diplomat Georgi Markov, who was killed with a ricin-imbedded pellet launched from an umbrella.

"One can never rule out the use of an exotic methods altogether, but such methods will continue to be rare, I suspect," he said.

Perhaps more alarming is the idea of using a bioweapon to target certain groups that have shared inherited traits. For now, Block said that threat remains low.

"I suspect the time will come when tailored bioweapons will become a serious possibility," he said. "We are not quite there yet, in my opinion."

-- Gina Harkins can be reached at gina.harkins@military.com. Follow her on Twitter @ginaaharkins.