Author's note: Sincere thanks to those who assisted me with this post; their assistance has made it safer and more compelling. An earlier but very similar version of this post was posted on LessWrong some time ago.

Recently, there has been an alarming development in the field of terrorist attacks; more and more terrorists seem to be committing attacks via crashing vehicles, often large trucks, into crowds of people. This method has several advantages for an attacker - it is very easy to obtain a vehicle, it is very difficult for police to protect against this sort of attack, and it does not particularly require special training on the part of the attacker.

While these attacks are an unwelcome development, I would like to propose an even more worrisome question - why didn't this happen sooner?

I see no reason to believe that there has been any particular technological development that has caused this method to become prevalent recently; trucks have been in mass production for over a hundred years. Similarly, terrorism itself is not particularly new - just look to the anarchist attacks of the late 19th and early 20th century. Why, then, weren't truck attacks being made earlier?

The answer, I think, is both simple and frightening. The types of people who make attacks hadn't thought of it yet. The main obstacle to these attacks was psychological and intellectual, not physical, and once attackers realized these methods were effective the number of attacks of this sort began increasing. If the Galleanists had realized this attack method was available, they might well have done it back in '21 -- but they didn't, and indeed nobody motivated to carry out these attacks seemed to until much later.

Another instance - though one with less lasting harm - pertains to Tylenol. In 1982, a criminal with unknown motives tampered with several Tylenol bottles, poisoning the capsules with cyanide and then replacing them on store shelves. Seven people died in the original attack, which caused a mass panic to the point where police cars were sent to drive down the streets broadcasting warnings against Tylenol from their loudspeakers; more people still were killed in later "copycat" crimes.

In this case, there was a better solution than with the truck rammings - in the aftermath of these events, greatly increased packaging security was put into place for over-the-counter medications. Capsules (which are comparatively easy to adulterate) fell out of favor somewhat in favor of tablets; further, pharmaceutical companies began putting tamper-resistant seals on their products and the government made product tampering a federal offense. Such attacks are now much harder to commit.

However, the core question remains - why was it that it took until 1982 for there to be a public attack like this, and then there were many more (TIME claims hundreds!) in short succession? The types of people who make attacks hadn't thought of it yet. Once the first attack and the panic around it exposed this vulnerability, opportunistic attackers carried out their own plans, and swift action suddenly became necessary - swift action to close a security hole that had been open for years and years!

One practical implication of this phenomenon is quite worrisome - one must be very careful to avoid accidentally spreading dangerous information. If the main constraint on an attack vector can really just be that the types of people who make attacks haven't thought of it yet, it's very important to avoid spreading knowledge of potential ways in which we're vulnerable to these attacks - you might wind up giving the wrong person dangerous ideas!

Many otherwise analytical or strategic thinkers that I have encountered seem to fall prey to the typical mind fallacy in these cases, assuming that others will also have put thought into these things and thus that there's no real risk in discussing them - after all, these methods are "obvious" or even "publicly known". Certainly I have made this mistake myself before!

However, what is "publicly known" in some book or white paper somewhere may only be practically known by a few people. Openly discussing such matters, especially online, risks many more people seeing it than otherwise would. Further, I would generally say that the types of people who make attacks are cunning but unimaginative. They are able to execute existing plans fairly effectively, but are comparatively unlikely to come up with novel methods. This means that there's extra reason to be wary that you might have come up with something they haven't.

Thus, when dealing with potentially dangerous information, care should be taken to prevent it from spreading. That doesn't, of course, mean that you can't talk these matters over with trusted colleagues or study to help prepare defenses and solve vulnerabilities - but it does mean that you should be careful when doing so.

This consideration is especially relevant to the effective altruist community because several issues discussed in effective altruism have the potential to be quite hazardous, especially those related to existential risks.

As strange as it seems, it is very possible that the only reason things haven't gone wrong in just the way you're thinking of is that dangerous people haven't thought of it yet - and if so, you don't want to be the one giving them ideas!

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This is an interesting issue.

I remember commentators discussing the question of why we didn't see i) terrorists shooting people at shopping centres, ii) knifing them, iii) running pedestrians over with cars, etc, all the way back in 2001-2005.

I find it surprising that this obvious idea would occur to me and other random journalists and bloggers, but not to people who are actually trying to engage in terrorism. Regardless, pointing out these methods didn't have any noticeable effect at the time.

An alternative explanation might be that we saw this spate of terrorism - as far as I know all committed by people who are sympathetic to ISIS - because ISIS had a different ideology that regarded these attacks as more worthwhile. My impression is that ISIS was more motivated by pure bloodthirsty religious zealotry, with less of an emphasis on shifting the foreign policy of the US and countries in the Middle-East.

It wouldn't surprise me if ISIS - with its indiscriminate enthusiasm for all forms of murder - was pushing these methods aggressively, while Al-Qaida and other predecessor groups would have regarded running over a few pedestrians as an insufficient reason for one of its supporters to die. Perhaps because it's not striking enough, embarrassingly unimpressive compared to 9/11, not focussed on the right symbolic targets, or for some other practical reason.

The copy-cat explanation is also slightly different from giving people 'ideas'. ISIS supporters may not have been motivated by a blog post mentioning the method - only by seeing someone else actually pull it off. One might think of these methods not only coming to people's attention, but also becoming 'fashionable' among a particular group of fanatics.

ISIS, with its quasi-country status, may also simply have been unusually effective at attracting supporters in Europe or the US, and convincing them to attempt terrorist attacks. We would naturally see more experimentation of all kinds when 1,000 people are actively working to kill their fellow civilians than when only 100 are.

I agree with your conclusion though - saying things that are 'obvious' can absolutely speed up how many people notice them. If only because there are many many possible 'obvious' thoughts, but with one stream of consciousness, each of us only has time to stumble on a tiny fraction.

Good points!

One note I'll add is that similar attacks with vehicles or bladed weapons were used against Israel prior to their adoption by ISIS, though these attacks are not as widely reported by Western media since they don't happen in Europe or the US; that said, it's quite possible that ISIS themselves got the idea from Palestinian attackers, especially if the "copycat hypothesis" is true.

The clearest explanation seems to be that extremely few people, terrorists included, are seriously trying to figure out the most effective ways to kill strangers - if they were, they'd be doing a better job of it.

AI Impacts' discontinuous progress investigation finds that it's really hard to make sudden progress on metrics that anyone cares about, because the low hanging fruit will already be gone. I doubt national militaries routinely miss effective ways to conduct war - when they make a serious effort, they find the best weapons.

If terrorists aren't noticing the most effective ways to maximize their damage, it could be good evidence that they're not seriously trying. (So +1 to Gwern's theory)

I actually quite disagree - I believe history indicates national militaries very frequently miss effective ways to conduct war. There's a famous phrase, "fighting the last war", that describes how military planners almost always miss innovations and changes in conditions during peacetime and only adapt when forced to by direct conflict.

For example, between World War One and World War Two, the world's militaries converged on several dangerously false theories with respect to what the next war would look like, and many weapons and strategies used in the early phases of World War Two were ineffective as a result.

Prior to World War Two it was widely believed that battleships were the decisive naval unit, that strategic bombing with large fleets of conventional bombers would be devastating and unstoppable, and that war would likely consist of battles across trenches and fixed fortifications.

By the end of World War Two, battleships were not only not the decisive naval unit but altogether obsolete in favor of aircraft carriers; strategic bombing wasted the lives of many soldiers, killed civilians indiscriminately, and didn't even work; fixed fortifications infamously failed and were no longer considered serious defenses.

I am quite confident that similar mistakes are being made now, and could even point you to some likely suspects if you like - and all this despite very substantial effort into arms development!

Good point, I hadn't considered that. If I were to try to fit this to my model, I would say that there's nobody really looking to produce the best military technology/tactics in between wars. But if you look at a period of sustained effort in staying on the military cutting edge, i.e. the Cold War, you won't see as many of these mistakes and you'll instead find fairly continuous progress with both sides continuously using the best available military technology. I'm not sure if this is actually a good interpretation, but it seems possible. (I'd be interested in where you think we're failing today!)

But even if this is true, your original claim remains true: if it takes a Cold War-level of vigilance to stay on the cutting edge, then terrorists probably aren't deploying the best available weaponry, just because they don't know about it.

So maybe an exceptional effort can keep you on the cutting edge, but terrorist groups aren't at that cutting edge?

Not entirely applicable to the discussion, but I just like talking about things like this and I finally found something tangentially related. Feel free to disregard.

if you look at a period of sustained effort in staying on the military cutting edge, i.e. the Cold War, you won't see as many of these mistakes and you'll instead find fairly continuous progress

The cold war wasn't peacetime though... there was continuous fighting by both sides. The Americans and Chinese in Korea, the Americans in Vietnam, and the Russians in Afghanistan.

One can argue that these places don't scale to the kind of military techniques and science that a World War 3 scenario would require. But this kind of war has never occurred with modern technology (specifically hydrogen bombs). How do we know that all of the ideas dreamed up by generals and military experts wouldn't get tossed out the window the moment it was determined that they were inapplicable to a nuclear war?

Thank you for this excellent analysis of dangerous information. The question has long been asked of attacks and murders of albino people in Tanzania and elsewhere: why did this become a shockingly common occurrence after 2007?

Previously there had been numerous instances of persecution, violent incidents involving people with various disabilities, accusations of and associations with disability and witchcraft, even incidents involving albinos. But after a report appeared in a local paper in Northern Tanzania was picked up by the BBC, there was an explosion in attacks, and they are still happening in 2019. Such attacks have since occurred in many other countries.

As the number of attacks rose rapidly, so did the number of articles about these attacks. A pattern emerged: 'witchcraft', rich clients who wanted to be richer, 'middlemen' who would carry out the attacks, large amounts of money being paid for albino body parts and organs. It's difficult to say, now, whether the attacks started to imitate the reports, or whether the reports accurately described the attacks. But after more than 10 years, there is still little more than speculation about who the clients might be, whether there really is a 'thriving trade' in body parts, etc, as claimed in the press.

There have been other related phenomena, enthusiastically reported in the press over the years, such as trade in and 'trafficking' of human organs, use of human body parts in 'witchcraft', use of children's body parts and organs, whole human and child sacrifice (by 'Satanists'), attacks on bald men for their organs and body parts, attacks on people for their genitals, use of human blood in occult practices, use of human skin in occult practices, and so on.

There seems to be something about the way that the stories of attacks on albinos were packaged that kept them on the front page for years. And the bulk of media articles on the subject merely copy or paraphrase what is found in other media articles. But much of the media coverage appears to be putting a price on the heads of albinos.

Which is where your analysis of dangerous information comes in. I've been based in Tanzania for much of the last 10 years and I have been researching this phenomenon for about 8 years. And I still conclude that the way the press covered these incidents, and continue to cover them, may be fanning the flames. I'd love to hear your comments.

IT organizations offer bug bounty programs. Why do governments not offer similar programs to fix vulnerabilities before they are exploited by terrorists?

It's general easy for an IT organization to fix a bug once the bug is disclosed. It's not easy to close are vulnerabilities of physical security that might be discovered.

Closing what was revealed on would be very expensive in contrast to the work required to come up with the ideas.

If it was feasible (and I'm a little bit skeptical), a 'social safety bugs' program rewarding people for sharing destructive ideas could be useful even if the 'bugs' were hard fix, by identifying them beforehand, by raising awareness of this problem of dangerous information, and perhaps even by using the frequency of repetitions of an idea as a proxy to measure how spread it is among the population. Couldn't it misfire? I mean, do dangerous people know they could be more effective if they researched a little bit more on new ways to do harm? Wouldn't they start crowdsourcing it or something, if they knew it? If they don't, the problem of dangerous info is a dangerous info, and we should be careful with raising awareness of it, too.

In general, I think the degree of compliance with any social norm one typically observes should be surprising. I've long thought it's remarkable that people intent on harming others do not use cars as weapons of destruction as much as they have recently. So I think there's something disturbing and something encouraging about this, in that we see lots of facile ways to hurt others be far rarer than we would expect in the presence of perfect information.

So what do we think about brilliant crime novelists and screenplay writers?

If a romance gives an idea easy to prevent, they might be overall helpful by raising awareness about this problem, so making it common knowledge.

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Does this include 9/11? I mean, hijacking planes to use them as bombers was an available strategy way before 9/11. Nassim Taleb begins a book (Black Swan?) imagining what would have happened if a legislator had passed a bill that would avoid it before 2001... We would never realize how many lives it'd have spared. And that's the most tragic to me: a wrongdoer needs only to get a new idea for an effective way of spreading destruction, but we would have a hard time to convince people that Tylenol poisoning is an eminent threat before many people died. Perhaps we could mitigate this risk if there were an institution to gather those destructive ideas, analyze them, and recommend strategies to authorities for mitigating those risks. Also, I think it's implicit, but maybe it should be openly stated: internet has made this problem worse, since it's made it easy to spread widely this type of idea.