Or search msdn for "This API is not intended to be used directly from your code" for examples of other APIs that are 'private' to Microsoft and will similarly get you booted.
Going back in time, there were (still are) a great many dlls and services in Windows with unnamed exports and not available to the general public (eg win32k, csrss, milcore etc).
Go back to the dark ages and as others have already mentioned there's the famous AARD example that used undocumented DOS data structures to distinguish MS-DOS from other variants.
Like I said, nothing new.