You may know that it is possible for USB devices to be created that do malicious things to your PC by committing deceptions right at the USB protocol level. This kind of thing cannot be defeated by antivirus software or erased by, for example, reformatting a USB stick. For example, a device that is labelled as a USB storage stick could actually identify to the PC as two devices, one the actual storage device and the other a keyboard, that feeds malicious keystrokes at carefully-chosen times. Alternatively, it can detect when the PC is booting, and activate a separate partition containing a virus, which is otherwise invisible to antivirus software, at only that point. More details about such possibilities are available here <https://opensource.srlabs.de/projects/badusb>. Here <https://github.com/robertfisk/USG/wiki> is an interesting project to create a hardware device that will act as a “firewall” for untrusted USB devices, to prevent malicious protocol exchanges from occurring between them and your PC. If you don’t want to build your own, there’s a link in the readme to buy NZ-made ones.