MAC address no longer in UID?

["Dean, James L" <jdean@lsumc.edu>]

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With Windows 2000, Microsoft claims UuidCreate no longer inserts a machine's
MAC address in UID strings.  Is this true?  (If so, how is the UID made
specific to a location and time)?  Or, is the MAC enciphered with the
date/time and some secret, making it available to those that know the
secret?