It appears there are many diff kinds of GUIDs -
Originally, GUIDs were designed to be used with ActiveX controls, but can beused for any purpose that requires a unique serial number. The Windowssystem calls "UuidCreate" or "CoCreateGuid" are used to make new GUIDs.The 128 bit GUID is mostly used in Windows to identify ActiveX controls. The low 48-bits of a GUID are usually the Ethernet adapter address. Because no 2 machines should have the same Ethernet adapter address, a GUID generated on one computer should not be duplicated on any other computer.
Ethernet cards, NIC cards, and the MAC:
NOTE* Technically, a modem PPP connection doesnt have and Ethernet adapter, so Windows seems to use a pseudo-Ethernet address from a modem PPP connection. On several diff computers that I checked, this address is the same number, 44-45-53-54-00-00. (To look it up yourself read bellow) Unlike the most business computer users, the typical home user probably does not don't have an Ethernet adapter (NIC card) in their computer-YET. But if you DO,then you show know that each NIC card has a BUILD-IN unique, identifiable addresss called network adress-i.e MAC.Without one, your Word and Excel documents will not be marked with a traceable GUID. However as MORE people switch over to using cable modems and ADSL modems for their Internet access, fingerprinting of documents will become much more likely even for the home user.
To understand the issues, I will list a few places where the GUID number can be found along with a few fun experiments.