A term used by Microsoft for a number that its programming generates to create a unique identifier for objects, such as a Word document. Furthermore, each Windows computer has its own GUID identifying it as being unique. Moreover, every time a user account is created, a GUID is assigned to the user. In 1999, Microsoft got into trouble for automatically shipping the GUIDs as part of the software registration process.

Privacy advocates raised concerens about the potential for abuse of GUIDs. In March 1999, a request was made to the U.S. Federal Trade Commission to investigate MicrosoftÂ’s use of GUIDs.

The problem raised was particularly related to the use of GUIDs in Office 97 and Office 2000 files, as the GUID numbers generated for Office documents on MacIntosh computers and networked PCs were found to incorporate the unique identification number of the computerÂ’s network card. The fact that Office documents contained a GUID remained hidden from the users, thus keeping them unaware that documents could be traced back to the computer that was used to create them. During this period, there were a number of reported incidents in which the creator of a document could be traced by the GUID in the document, including circumstances where the author had taken great care to maintain anonymity.