To get to work in the morning, Omar Akbari has to pass through a minimum of six sealed doors, including an air-locked vestibule. The UC Riverside entomologist studies the world’s deadliest creature: the Aedes aegypti mosquito, whose bite transmits diseases that kill millions each year. But that’s not the reason for all the extra security. Akbari isn’t just studying mosquitoes—he’s re-engineering them with self-destruct switches. And that’s not something you want accidentally escaping into the world.

The technology Akbari is designing is something called a gene drive. Think of it as a way to supercharge evolution, forcing a genetic modification to spread through an entire population in just a few generations. Scientists see it as a powerful tool that could finally vanquish diseases like malaria, dengue, and Zika. But US defense agencies see something else: a national security issue.

Last year, former director of national intelligence James Clapper added gene editing to a list of threats posed by “weapons of mass destruction and proliferation.” In July, the US Defense Advanced Research Projects Agency awarded $65 million in four-year contracts to seven teams of scientists, including Akbari, to study gene-editing technologies. The commitment officially made Darpa the world’s largest government funder of gene drive research. Most of that money is going toward designing safer systems and developing tools to counter rogue gene drives that might get into the environment either by accident, or with malicious intent.

That danger may be more real than scientists first thought. Four years ago, when Harvard biologist Kevin Esvelt first suggested the idea of building gene drives with the newly discovered Crispr gene editing system, he was thinking about extinction. Specifically, preventing endangered wildlife from disappearing by spreading a fertility-reducing gene through the invasive animals competing with them for resources. Conservation biologists took the idea and ran with it; they're now considering gene drives to save native birds in Hawaii, New Zealand, and the Farallones. But now, Esvelt is saying they should slow down.

That's based on the results of a new mathematical model he and his colleagues published on Thursday on the bioRxiv preprint server. Taking into account things like how often Crispr screws up and the likelihood of protective mutations arising, their work shows how gene drives could be ruthlessly aggressive. Just a few engineered organisms could irrevocably alter an ecosystem. While Esvelt doesn't view the technology as inherently threatening, he is now preaching that it deserves a bold new caution in how it's applied.

"The primary risk posed by gene drive technology is social," he says. "Unethical closed-door research, unwarranted fears, or unauthorized releases of gene drives will damage public trust in science and governance." He still thinks gene drives have potential to save threatened species and battle public health threats. But researchers will have to invent safer forms of the technology first. That's where the Darpa money comes in. Until very recently, gene drives have been largely theoretical—safe ones even more so. But with the new funds, scientists like Esvelt and Akbari are starting to put together the pieces to test them in real life. That starts with bugs that have a gene editor baked into their DNA from the moment of conception. In a paper published Tuesday in the Proceedings of the National Academy of Sciences, Akbari did that for the first time in Aedes aegypti, creating mosquitoes encoded with the bacterial Cas9 enzyme.