Genome editing is a weapon of mass destruction.

That’s according to James Clapper, U.S. director of national intelligence, who on Tuesday, in the annual worldwide threat assessment report of the U.S. intelligence community, added gene editing to a list of threats posed by “weapons of mass destruction and proliferation.”

Gene editing refers to several novel ways to alter the DNA inside living cells. The most popular method, CRISPR, has been revolutionizing scientific research, leading to novel animals and crops, and is likely to power a new generation of gene treatments for serious diseases (see “Everything You Need to Know About CRISPR’s Monster Year”).

It is gene editing’s relative ease of use that worries the U.S. intelligence community, according to the assessment. “Given the broad distribution, low cost, and accelerated pace of development of this dual-use technology, its deliberate or unintentional misuse might lead to far-reaching economic and national security implications,” the report said.

The choice by the U.S. spy chief to call out gene editing as a potential weapon of mass destruction, or WMD, surprised some experts. It was the only biotechnology appearing in a tally of six more conventional threats, like North Korea’s suspected nuclear detonation on January 6, Syria’s undeclared chemical weapons, and new Russian cruise missiles that might violate an international treaty.

James Clapper, the U.S. director of national intelligence, oversees spying agencies with a combined budget of more than $50 billion.

The report is an unclassified version of the “collective insights” of the Central Intelligence Agency, the National Security Agency, and half a dozen other U.S. spy and fact-gathering operations.

Although the report doesn’t mention CRISPR by name, Clapper clearly had the newest and the most versatile of the gene-editing systems in mind. The CRISPR technique’s low cost and relative ease of use—the basic ingredients can be bought online for $60—seems to have spooked intelligence agencies.

“Research in genome editing conducted by countries with different regulatory or ethical standards than those of Western countries probably increases the risk of the creation of potentially harmful biological agents or products,” the report said.

The concern is that biotechnology is a “dual use” technology—meaning normal scientific developments could also be harnessed as weapons. The report noted that new discoveries “move easily in the globalized economy, as do personnel with the scientific expertise to design and use them.”

Clapper didn’t lay out any particular bioweapons scenarios, but scientists have previously speculated about whether CRISPR could be used to make “killer mosquitoes,” plagues that wipe out staple crops, or even a virus that snips at people’s DNA.

“Biotechnology, more than any other domain, has great potential for human good, but also has the possibility to be misused,” says Daniel Gerstein, a senior policy analyst at RAND and a former under secretary at the Department of Homeland Defense. “We are worried about people developing some sort of pathogen with robust capabilities, but we are also concerned about the chance of misutilization. We could have an accident occur with gene editing that is catastrophic, since the genome is the very essence of life.”

Piers Millet, an expert on bioweapons at the Woodrow Wilson Center in Washington, D.C., says Clapper’s singling out of gene editing on the WMD list was “a surprise,” since making a bioweapon—say, an extra-virulent form of anthrax—still requires mastery of a “wide raft of technologies.”

Development of bioweapons is banned by the Biological and Toxin Weapons Convention, a Cold War–era treaty that outlawed biological warfare programs. The U.S., China, Russia, and 172 other countries have signed it. Millet says that experts who met in Warsaw last September to discuss the treaty felt a threat from terrorist groups was still remote, given the complexity of producing a bioweapon. Millet says the group concluded that “for the foreseeable future, such applications are only within the grasp of states.”

The intelligence assessment drew specific attention to the possibility of using CRISPR to edit the DNA of human embryos to produce genetic changes in the next generation of people—for example, to remove disease risks. It noted that fast advances in genome editing in 2015 compelled “groups of high-profile U.S. and European biologists to question unregulated editing of the human germ line (cells that are relevant for reproduction), which might create inheritable genetic changes.”

So far, the debate over changing the next generation’s genes has been mostly an ethical question, and the report didn’t say how such a development would be considered a WMD, although it’s possible to imagine a virus designed to kill or injure people by altering their genomes.