It's been done. It's rare, but not as rare as you might think.

The biggest risk is your wi-fi and bluetooth connections- if you aren't using them, TURN THEM OFF. Not only are they sucking up a bunch of power, but they want to hop into bed with device that sweet talks them. Yes, the security has improved in the past few years, but bluetooth is still pretty promiscous. It's not so much what you could catch, but what could be borrowed.