I stumbled upon this article titled "The Illusions of Vista" which states that Microsoft's newest version of Windows, Vista, keeps hidden files that are several *gigabytes* in size so that a user can restore any file to any previous point in its development.  Apparently all versions of Vista keep these files, but only people using the business edition can access those files to do "magic" restorations.

It occurred to me that a majority of ordinary users of Vista would be unaware of all these hidden files and what they contained.  It seems to me that Bill Gates and company have created quite a resource for knowledgeable spies.