But the new breed of Isil terrorists is different. They tend to be young men, many of them British, who are masters of computer hacking. They conceal themselves in cyberspace by blending in perfectly. Not so long ago, looking for a jihadi on the internet was like looking for a needle in a haystack: they’d stand out by behaving oddly, taking a few too many steps to cover their tracks. Now, it’s like looking for a specific piece of hay in a haystack. The bad guys use standard email programmes that you can download from iTunes, with keys that are unknown even to the provider. Email encryption has become standard; nowadays, everyone is hiding. Which makes jihadi-hunting all the more difficult.