During a physical penetration test, it is not uncommon for the tester (attacker) to drop usb thumb drives out in the parking lot or someplace within the building. The hope is that an employee will pick it up and connect it to their computer. The end goal: malware that makes a connection back to the attacker.
more here..........http://blog.secureideas.com/2014/10/thumb-drives-can-you-tell-difference.html
more here..........http://blog.secureideas.com/2014/10/thumb-drives-can-you-tell-difference.html