1. A method of restoring an operational state of a computer entity, said computer entity comprising: at least one data processor; at least one data storage device; a primary operating system capable of running said computer entity; a secondary operating system capable of rebuilding said primary operating system; and a copy of said primary operating system in an as manufactured state, stored on said data storage device; said method comprising the steps of: booting said computer entity to operate from said secondary operating system; and under control of said secondary operating system, rebuilding said primary operating system from said copy of said primary operating system.