GSM networks, cell phones are subject to hacking attacks.

Cellphones running on popular GSM wireless networks around the globe are vulnerable to hijacking attempts, a German security expert says. Although T-mobile ranks as the most secure GSM network in the U.S., other networks have no security measures that can limit exploits against GSM phones. About 80 percent of the world’s cell phones run on GSM, although – in the U.S. – new networks such as CDMA have become predominant.

Americans who travel to other countries often choose GSM networks like AT&T and T-Mobile because they can use their phones on foreign networks. Though they might be able to use their phone as-is in other countries, they can also buy SIM cards that allow their phones to connect to local wireless networks without paying expensive international roaming charges.