Original URL: http://www.theregister.co.uk/2011/02/04/silent_sms/
Dutch get wound up over invisible SMS
Smoking a little too much?
Dutch tabloid De Telegraaf reports that 12 Somalis picked up in Amsterdam over Christmas were located using secret SMS messages, apparently bouncing back their GPS coordinates for the authorities.
The 12 suspects were arrested on Christmas eve following a tip-off that they were planning some sort of terrorist attack, but now De Telegraaf reveals that in order to make those arrests the local security forces relied on a hitherto secret capability to track mobile phones  through the use of silent SMS messages.
Using the still-secret capability apparently required special permission – provided to the Algemene Inlichtingen- en Veiligheidsdienst (Intelligence and Security Department) – and enabled the security forces to send out SMS messages to the suspects' phones, which helpfully reported back with their GPS coordinates and enabled swift arrest. But while that capability may worry some, it is really limited compared to what the security forces can really do.
Silent SMS messages are indeed part of the GSM standard, and they can be directed to the handset or SIM without alerting the user. Handset-targeted messages are used to alert the phone that an MMS message is waiting for it, among other things, while those addressed to the SIM often contain changes to preferred roaming partners, but could conceivably contain a request for location information – if the SIM had previously been configured to respond to such a request.
But there would be no point; network operators already know where every phone is – they have to in order to deliver the phone calls. In Europe network operators are also required to store that data , enabling the Algemene Inlichtingen- en Veiligheidsdienst – or any similar organisation – to find out not just where their suspects are, but everywhere their suspects have been for the last 12 months.
Providing that information in real time isn't hard, though UK operators are permitted to bill the security forces for the effort involved, so there's really no need to muck about sending secret SMS messages or relying on handsets equipped with GPS, when a text to the network operator would be so much more effective. ®