A GUID (global unique identifier) is a term used by Microsoft for a number that its programming generates to create a unique identity for an entity such as a Word document. GUIDs are widely used in Microsoft products to identify interfaces, replica sets, records, and other objects. Different kinds of objects have different kinds

of GUIDs – for instance, a Microsoft Access database uses a 16-byte field to establish a unique identifier for replication.

The nature of certain of Microsoft’s GUIDs, the use made of GUIDs, and the potential for abuse arising out of GUIDs, have raised concern among privacy advocates. In March, 1999, a request was made to the U.S. Federal Trade Commission to investigate Microsoft’s use of GUIDs.

The controversy relates especially to GUIDs attached to Office 97 and Office 2000 documents. The GUID numbers generated for Office documents on Mac and networked PCs have been found to incorporate the unique identification number of the computer’s card. The fact that Office documents, such as a Word file or an Excel spreadsheet, contain a GUID is not made evident to users. There are a number of reported incidents in which the author of a document could be traced by the GUID in the document, even in circumstances where the author had taken exceptional care to maintain their anonymity.

In response to expressed concerns, Microsoft has released a patch for Office 97 SR2 which disables the GUID function, and a utility to remove GUIDs from existing documents.
Concerns about the GUID parallel similar concerns about the potential for abuse of Intel’s processor serial number.