Trend Micro experts spotted a new variant of ZBOT Malware which is capable of spreading itself automatically via USB Flash Drives or removable drives. The malware family itself is frequently updated with mechanisms designed to evade detection by antivirus and network security appliances. This particular variant arrives through a malicious PDF file disguised as a sales invoice document and when user opens this file using Adobe Reader, it triggers an exploit. It also has an auto update module, so that it can download and run an updated copy of itself.
Source: https://thehackernews.com/2013/06/ZeuS-Malware-antivirus-usb-free-spyware.html