Software Hack Lets Feature Phones Jam Calls, Texts Within 75 Miles

There's something uniquely scary about the idea of your calls being jammed. Good news! It turns out blocking calls and texts to certain phones is pretty easy. Hackers have figured out how to turn a feature phone into a "jammer" with just a few software modifications.

The hack was developed by a security research group at the Technical University of Berlin, who shared their findings in a recent paper at the Usenix Security Symposium in Washington, D.C., last week. Basically, with the help of custom firmware, one feature phone can block calls and texts around it for about 75 square miles by stealing the communications and spiking them into the ground.

When an SMS or call goes out over 2G GSM, the tower starts the exchange by pinging the receiving phone. Once the receiving phone answers back, then the SMS or call goes through. These jammers work by answering the tower's ping before the right phone can. It's not technically "jamming" but the effect is the same. The researchers didn't design the hack to actually read the stolen communications, but there's no reason they couldn't.

Fortunately, there are a few catches. So far it seems that Motorola phones are the only ones able to be turned into these jammers. Also the jammers only work on 2G GSM networks, and can only block calls and texts to phones of the same provider. So a T-Mobile jammer can only block calls to other T-Mobile phones, and CDMA carriers like Verizon and Sprint are safe.

This jamming technique also can't touch 3G or 4G data, but for the time being both T-Mobile and AT&T rely on blockable 2G GSM for texts and calls. There's no record of anyone putting this strategy to use yet, but the fact that it can exist means that 2G GSM networks aren't a safe, reliable bet for calls and texts anymore.

It's certainly not the end of the world, but knowing that even a subset of calls and texts in an area could be blocked with such ease is troubling, especially in an emergency situation. But just keep an eye on Twitter, and you should be all right. [MIT Technology Review]