In well designed USB port you'd at least have diodes shorting it to ground/vcc. But they are designed for ESD protection, so while high voltage, not that much

In well designed USB port you'd at least have diodes shorting it to ground/vcc. But they are designed for ESD protection, so while high voltage, not that much energy The problem is that there is no fuses, while ethernet basically have transformer working as a fuse, USBkiller can hammer the protection diodes till they burn out and then the rest of it gets it.