Be careful what you stick it into.
The USB ports on a computer present a security risk. Not only are storage devices able to plug in and interface with the hardware, but also coffee cup warmers, fans, and even mini-vacuums.
A team of computer engineers from Royal Military College of Canada in Kingston, Ontario exploited a weakness in the USB plug-and-play functionality. What the team did was create a fake USB device that reported itself as something that computer already recognized.
For example, if the computer already paired itself with a USB camera, a hacker could spoof the same identity on another device.
As a proof of concept, the team designed a USB keyboard that contained a circuit that stole data from the hard drive and transmitted it by flashing an LED in a morse code-like fashion, as well as through sounds output by the sound card. While such methods are hugely inefficient and likely ineffective, it was just a proof of concept of the vulnerability.
Even though virus scanning software may check USB storage for malware, secretly planted trojans inside USB peripherals will likely be missed.
"We've shown any USB device could contain a hardware trojan," said Sylvain Leblanc, one of the engineers. "You could mount a hardware trojan attack with a USB coffee-cup warmer."
(source: New Scientist.)