SOME things are best kept secret. It is hard, for instance, to argue that public interest dictates publishing the blueprints for an atom bomb. The matter is less clear-cut, however, when scientific information that has the potential to wreak havoc might also stop that havoc happening.

Take bird flu. It has killed more than 330 people since 2003. That may not sound many, but it amounts to 60% of the 570 known cases of the disease. The only reason the death toll is not higher is that those who succumbed caught the virus directly from a bird (usually a chicken). Fortunately for everyone else, it does not pass easily from person to person.

But it might. That is the burden of research carried out last year by two teams of scientists, one in America and one in the Netherlands. They tweaked the bird-flu virus's genes to produce a version which can travel through the air from ferret to ferret. And ferrets are, in this context, good proxies for people.

The researchers' motives were pure. The mutations they combined to produce their ferret-killing flu virus are all out there in the wild already. There is every chance those mutations could get together naturally and unleash a pandemic. By anticipating that recombination the two teams highlighted the risk, gave vaccine researchers a head start in thinking about how to counter it and, by fingering the mutations, spurred surveillance efforts, which have often been half-hearted.

Or, rather, they would have done had they been allowed to publish their results. They weren't. Both the American and the Dutch governments saw not a sensible anticipation of a threat, but a threat in its own right. Their fear was that bad guys somewhere might repeat the experiment and weaponise the result. So in December they banned publication of the papers revealing the technical details of what the teams had done.

The threat from influenza is real. So-called Spanish flu, which infected 500m people in 1918-19, claimed the lives of one in five of those who caught it. Subsequent flu epidemics, though not as bad, have still cut swathes through humanity whenever they have arisen. But terrorism is real, too. Though there is no known case of biological warfare in the past 100 years, many countries have experimented with the idea; and there is concern that some terrorist groups, motivated not by specific political grievances but by a general hatred of the West, might unleash the uncontrollable mayhem of a viral epidemic purely out of spite. So who is right—the researchers who want to publish their findings, or the governments that want to stop them?

In this particular case, probably the researchers. And, to their credit, the authorities seem to have recognised that. After months of fraught deliberation involving the world's leading virologists, journal editors, security experts, ethicists and policymakers, the Americans reversed their stance on April 20th (see article). The Dutch were reconsidering theirs as The Economist went to press.

The reason is that, as bioterrorists go, humans pale in comparison with nature. Even America's security services, which might be expected to err on the side of caution, seem to agree that the odds of a bioterror attack are long. Biological weapons require skilled scientists working in state-of-the-art facilities. Even then, they are unpredictable—and therefore difficult to control. A deadly bug might come back to bite its maker, possibly before it had been made into a weapon. Aum Shinrikyo, a sect with sophisticated scientific capability, toyed with anthrax in 1993. But for its most brazen attack, when it killed 13 people in the Tokyo metro two years later, it preferred nerve gas. In September 2001 al-Qaeda plumped for aeroplanes.

Nature, by contrast, has form in this area. From the Black Death via Spanish flu to AIDS, bacteria and viruses have killed on a scale that terrorists and dictators can only dream of. The more you gag scientists or hide data, the harder it is for them to look for cures; you also probably drive bright young researchers away towards less fraught, blander areas.

Natural-born killers

At the moment, then, the natural threat seems greater than the artificial one. And it is brave of America's authorities to recognise that. If a terrorist outrage does happen, they will surely get the blame. By contrast, “acts of nature” are more easily shrugged off as, as it were, acts of God.

This case does, however, highlight a problem that is only going to grow. The atom bomb is a child of physics. Nerve gas is a child of chemistry. These are both old, mature sciences. Biotechnology is new. Its potential and limits are obscure. This time America has made the right decision. It is to be hoped that the Dutch will soon follow suit. But it behoves everyone—politicians and scientists alike—to keep a close eye on a fast-changing technology and on any shift in the balance of risks.