The ZERO has a built-in USB-C port that can be used for two things only: charging, and firmware updates. Unless the ZERO is in 'update mode', data transfer via the USB-C port is impossible.
Moreover, the USB-C port is isolated from the rest of the device for security reasons. This means that to enable USB, you have to reboot the device. In this ‘update mode’ the ZERO will only receive packages and the USB will be sandboxed from any other part of the device, including any part that contains sensitive data.
Before installing an update the secure firmware will check the new package for its genuineness, display a warning if it’s not, and otherwise boot back in normal operating mode with USB transfers fully disabled again.
The USB-C port is also protected by the EAL7 certified secure OS. This means it has passed the most extreme security tests, up to a level higher than average banks and governments (which are typically EAL5 certified).
Your security is our greatest concern.