About two weeks ago two security researchers, Adam Caudill and Brandon Wilson, released the code to a USB exploit virus BadUSB. BadUSB is a malicious firmware exploit which, if infected with, could effectivly ruin your computer. The code to the exploit is posted to Github by Adam Caudill.
In the recent Wired article "That Unpatchable USB Malware Now Has a Patch. . . Sort Of", Caudill talks about the many limitations of this particular 'fix' to BadUSB. Part of the fix involves opening up the USB and applying a layer of epoxy glue to the insides of the USB, preventing the device from being reopened going forward. Caudill is quoted saying "What we’re doing today is about experimenting, learning what can be done, and hoping the community will join in these experiments and take it further."
BadUSB is unlikely to infect the average consumer, yet it is feared because currently no known virus scan and removal program can detect it. The best prevention is to only use USB devices that have been in your control the entire duration, which should always be best practice for USB devices. In the InfoWord article "The BadUSB exploit is deadly, but few may be hit", the author says that "BadUSB is the biggest threat you can be take off your panic list". While the threat is possible, it is far more likely you'll be hit by a virus running in your web browser.