There's something particularly scary about having your calls blocked. Good news! It turns out that blocking calls and texts to certain phones is quite simple. Hackers have figured out how to turn a feature phone into a "jammer" with just a few software tweaks.
The hack was developed by a security research group at the Technical University of Berlin, which shared its findings in a recent paper at the Usenix Security Symposium in Washington, D.C., last week. Basically, using custom firmware, a feature phone can block calls and texts around it for about 75 square miles by stealing communications and smashing them to the ground.
When an SMS or a call goes out on GSM 2G, the tower starts the exchange by sending a ping request to the receiving phone. Once the receiving phone answers, the SMS or call goes through. These jammers work by responding to the tower ping before the good phone can. It's not technically "jamming" but the effect is the same. The researchers didn't design the hack to read stolen communications, but there's no reason they couldn't.
Fortunately, there are a few catches. So far, it looks like Motorola phones are the only ones that can be turned into these phone jammer. Also, the jammers only work on 2G GSM networks and can only block calls and SMS to phones from the same provider. A T-Mobile jammer can therefore 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 now, T-Mobile and AT&T rely on blockable 2G GSM for texting and calling. No one has implemented this strategy yet, but the fact that it may exist means that 2G GSM networks are no longer a safe and reliable bet for calls and texts.
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 keep an eye on Twitter and you should be fine.