Ah, the humble SIM Card. While it might only be used by two of the four major carriers in the States, it's pretty much the de facto method of getting yourself connected wirelessly throughout most of Europe and even parts of Asia. SIM Cards are pretty amazing when you think about it - on their own they're quite useless but, together with your phone they take on a whole new power. Sure, most of us think about them as just different phone numbers but, they've got more in them than just a few digits.
Recently, Karsten Nohl of Security Research Labs has discovered that some SIM cards aren't as secure as others and that they can be taken over with just a couple of SMS messages, in a matter of minutes. The New York Times reports that Karsten discovered that sending an SMS to a SIM card while masquerading as a carrier, would result in an error message being returned. This only happened in roughly a quarter of cases but, the SMS would often content the info needed to crack the SIM's digital key. Once the key is cracked, another SMS is sent which gives access to the SIM, and along with it the ability to listen in on call, make purchases and more.
Karsten has said that this only applies to SIM cards that are somewhat older, and only carry the standard encryption of DES. Newer SIM Cards with Triple DES would spot the SMS message as a fraudulent one, instead of handing over the keys to the castle. The GSM Association have been given some data on the hack, which has then been passed to carriers and SIM manufacturers but, Nohl is planning to let the cat out of the bag at the Black Hat conference shortly. While this only affects older SIM Cards, it's estimated that as many as 750 Million users across the globe could be at risk. Let's just hope that networks work on a fix and that the details of this hack don't fall into the wrong hands.