The bad news is that even a hyper-vigilant society will not be able to head off all the self-made jihadis in the world. The good news is that the terror networks have largely been disrupted. The main threat these days comes from the do-it-yourselfers. Only a few of those angry young jihadis will try to act, and fewer still will succeed, and when they do succeed they probably won’t do much damage.

So why are we so prone to panic?

In Boston, the Americans shut down an entire city while they pursued the fugitives. I hope they don’t make a habit of this. Mass hysteria just emboldens other would-be martyrs to unleash their own mayhem. Since 9/11, we’ve allowed ourselves to become far too infantilized by the threat of terror. In Britain, there are new calls to expand the security state by monitoring people’s e-mail and Internet use. Societies that routinely deal with terror threats (such as Israel) are much more sensible. They do not shut down entire cities when bombs go off, or force hundreds of thousands of people to remove their shoes and discard their water bottles every day because of purely imaginary threats. When an attack happens, they efficiently scrape up the body parts and get on with life. (They also practise ruthless profiling.)