15 March, 2004: Unwanted calls

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Among reports of the murder of 201 commuters in Spain last week and of the results of yesterday's elections, one technical detail caught my eye: the revelation that, like in Bali and various ETA bombings, the bombs used in the killings were triggered by mobile phones. (As an aside, there has been much hasty commentary on how the attacks `caused' the fall of Jose Maria Aznar's government, and how this represents a craven appeasement of the terrorists, rather than Spaniards' legitimate exercise of their democratic rights. I think Christopher Sheil summed it up best, in a comment on Crooked Timber: ``If I'm reading the warbloggers right, their conclusion seems clear: we need to elect a new Spanish people.'' Enough said.)

This detail forms an interesting story about the unintended consequences of new technologies. Mobile phones are small, readily available, reliable, and probably easy to adapt into bomb triggers. (At a guess, I'd imagine that the terrorists would have wired the bomb detonators into the ringer or vibrating alert thingy on the phones, and then phoned or texted them at the time they wanted the bombs to explode. An alternative theory is that the phones' alarm clock features were used instead.)

Historically, many terrorist groups seem to have struggled with the technical challenges of bomb-making, or, more specifically, bomb triggering. Some readers will remember a 1996 IRA bus bombing, supposedly an accident which occurred when the perpetrator -- whose time-bomb was controlled by components scavenged from a video recorder -- misunderstood the 24-hour clock and blew himself up on the way to a target he intended to destroy the next morning, after he had made his escape. The `shoe bomber' Richard Reid showed even less technical prowess, being apprehended by his intended victims while he struggled to light a match and ignite the fuse of his diabolical footwear. One IRA `bomb factory' was -- apparently -- destroyed after the security services installed an induction loop in the ceiling; the bomb-makers, too ill-informed to twist the wires connected to their detonators, died for their mistake. Natural selection is, of course, a phenomenon of greater importance in bomb-making than other professions, and it seems that the IRA at least learned from these mistakes, though that didn't stop them from claiming that their Remembrance Day bomb at Enniskillen was triggered accidentally by a British Army radio jammer.

Mobile phones and the GSM network change all this. Even an inexperienced bomb-maker ought to be able to wire together phone and detonator; phones are reliable and the cautious terrorist can either use the thing's alarm clock to trigger the bomb, thereby avoiding anxiety about unintentionally lethal telemarketing calls, or make sure that only a call from his own phone number will cause the bomb to ring....

And there aren't any easy technical measures which can usefully be taken against this new application for GSM. With a couple of exceptions where phones aren't allowed or don't work -- notably on aeroplanes or in underground railways -- everywhere that people gather, presenting an attractive target for the political murderer, they also expect to be able to make and receive phone calls. From the perspective of the GSM network, a phone connected to a bomb is no different from a phone in someone's pocket.

While evidence from phones used in this way may help investigators a little in their detective work -- for instance, they can use network records to search for a phone which was in the location where a bomb exploded, received a call at the time of the explosion, and then went off-air, and then search for the caller -- that's not likely to help enormously, especially since the terrorist could trigger the bomb from anywhere in the world and take steps to conceal their identity when they did.

This use of mobile phones is likely to distress people a little, I suppose; the Mirror lead with the story Massacred by Mobiles, (at least it wasn't a story about GSM masts causing cancer) but this is the sort of thing we will, sadly, have to get used to as reliable wireless networking becomes pervasive. Nobody is going to claim that this threat outweighs the benefits of phones, but we'd better adjust to the fact that some of their uses are undesirable -- and inevitable. Probably the same will be true of other innovations, too.

Copyright (c) 2004 Chris Lightfoot; available under a Creative Commons License.