Due to security holes in the SMS protocol, it is possible to send text messages that allow a hacker to take over an Apple iPhone, according to Fortune:
Using a flaw they've found in the iPhone's handling of text messages, the researchers say they'll demonstrate how to send a series of mostly invisible SMS bursts that can give a hacker complete power over any of the smart phone's functions. That includes dialing the phone, visiting Web sites, turning on the device's camera and microphone and, most importantly, sending more text messages to further propagate a mass-gadget hijacking.
Want to be safe from this attack? Too bad. You can't turn off SMS texting on most phones, and Apple hasn't released a patch. Apparently the only hope is that no exploits have yet been seen in the wild. That, and turning off your phone immediately if someone sends you a single square as a text message.