He did claim "reformat", which tends to delete these viruses. Albeit to clarify you'd also need to clear the boot record, which is not something all DOS format

He did claim "reformat", which tends to delete these viruses. Albeit to clarify you'd also need to clear the boot record, which is not something all DOS format tools would do. Compare that to USB devices, which contain data that survives to all host-initiated methods of erasure and which may in fact not be storage devices at all; i.e. fake keyboard/mouse presses et al.