““If computers are readily accessible, and they have a floppy disk or CD drive, you might also consider fitting locks to floppy and CD drives, or (in extreme cases) removing the floppy and CD drives from the computers altogether. If the server or control room Stations have unused USB ports, they should be disabled to prevent memory sticks or other uncontrolled devices from being connected to the system. Such devices may be used to introduce virus or other malware. You should also consider disabling or physically protecting the power button to prevent unauthorized use.””
