ESET researchers have discovered a new data-stealer, dubbed USB Thief (Win32/PSW.Stealer.NAI), that relies on USB devices in order to spread itself. USB Thief is able to infect air-gapped or isolated systems does not leave any trace of activity on the infected systems. Malware authors have implemented special techniques to protect USB Thief from being detected and analyzed. The authors also implemented an advanced multi-staged encryption process to protect the Trojan.”]
Source: http://securityaffairs.co/wordpress/45741/malware/usb-thief-trojan.html