Last month, one of the top intelligence officials in the United States warned that genome-editing technology is now a potential weapon of mass destruction. Techniques such as the emerging CRISPR–Cas9 system, US director of national intelligence James Clapper warned in an annual threat-assessment report to the US Senate, should be listed as dangers alongside nuclear tests in North Korea or clandestine chemical weapons in Syria (see go.nature.com/jxuyev).

The headline message might scream ‘overreaction’ — and indeed most serious science commentators seem to have assumed as much and ignored Clapper’s hyperbole — but the terms he used to describe the technology seem uncontroversial. The US spooks describe the “broad distribution, low cost, and accelerated pace of development” of gene editing, and say that its “deliberate or unintentional” use could have “far-reaching economic and national security implications”.

“Research in genome editing,” the threat assessment continues, “increases the risk of the creation of potentially harmful biological agents or products.” And Clapper, naturally, points the finger at science in nations “with different regulatory or ethical standards than those of Western countries”. But for a glimpse of just how far-reaching the “deliberate or unintentional” use of gene editing could be, he need only look over his shoulder.

Last year, scientists in California reported that they had used gene editing (together with another new biotechnology called gene drive) to introduce a mutation that disabled both normal copies of a pigmentation gene on a fruit-fly chromosome. The change made the insects turn pale yellow — as did their offspring, their offspring’s offspring and so on. The change was so powerful that, had any of the California flies escaped, it has been estimated that somewhere between one in five and one in two of all the fruit flies in the world would be yellow today. The flies did not escape — but then, weapons of mass destruction are a political problem because they exist, not because they are deployed.

Clapper was anxious about the implications of gene editing because of its dual-use possibilities. But a binary outcome is inadequate for describing the spectrum of ways in which the CRISPR–Cas9 system is changing science and could benefit scientists and the public. In a special issue this week, we examine some of these.

Much of the early attention has focused on the prospect of human-embryo modification. The issues that such ‘germline’ changes could raise for current and future generations have, rightly, been intensely debated. But the uses of CRISPR–Cas9 with early promise are those in laboratories, not clinics — and in human somatic (non-reproductive) cells, bacteria, viruses, animals and plants, not in human germ cells. A pair of News Features explores these scenarios.

Genome editing is a science for which the alarm about how it could go wrong has largely lagged behind the hype over what good it could achieve — at least before Clapper had his say. And much of the hype has come from those in the know. The speed at which the biological community has adopted gene editing, and the range of applications that it is being used for, speak volumes about its potential. The possibilities — human–animal chimaeras for organ transplants, climate-change-proof crops, eradication of disease vectors — seem endless.

Among the many unknowns that swirl around the future of gene editing is the reaction of the wider public. To their credit, some scientists and organizations are making attempts to foster openness and discussion, on the topic of gene drives, for instance. It is crucial that these deliberations continue, and that such environmental issues are kept scientifically and ethically distinct from concerns relating to clinical applications.