Quote (via Forbes):

If you receive a text message on your iPhone any time after Thursday afternoon containing only a single square character, Charlie Miller would suggest you turn the device off. Quickly.

That small cipher will likely be your only warning that someone has taken advantage of a bug that Miller and his fellow cybersecurity researcher Collin Mulliner plan to publicize Thursday at the Black Hat cybersecurity conference in Las Vegas. 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.

“This is serious. The only thing you can do to prevent it is turn off your phone,” Miller told Forbes. “Someone could pretty quickly take over every iPhone in the world with this.”