U.S. Deputy Defense Secretary William Lynn says a single USB drive containing malicious code was inserted into a laptop computer. The malware, placed on the drive by a foreign intelligence agency, was uploaded to a network run by the military. It spread undetected on both classified and unclassified systems, establishing a “digital beachhead” The incident led to a massive Pentagon response operation called “Operation Buckshot Yankee” Lynn did not say whether the malware allowed any classified or unclassified data to be stolen from defense networks.”]
Source: https://www.csoonline.com/article/2125888/infected-usb-drive-blamed-for–08-military-breach.html