1. A method of creating and maintaining a hidden back-up operating system, comprising: copying a computer's primary operating system files to a location within an existing storage area that is not hidden during operation, to create back-up operating system files; altering configuration data in said back-up operating system files so as to reflect their location in said storage area; providing a file system filter driver operative to intercept access and enumeration requests directed to said back-up operating system files, and to fail said requests or edit the data returned, so as to hide said back-up operating system files from the requesting application; and booting said computer so as to load said file system filter driver.