Globally unique identifier

A globally unique identifier (GUID) is embedded in most computer hardware and some computer software. GUIDs were initially developed to provide security by removing the anonymity protection of malicious users. Because GUIDs were embedded in hardware, they could not be removed or altered by the user. However, the actual uses of GUIDs quickly because twofold. First, they were used by marketers to track user's online habits, much in the way a cookie is used. Second, some of the major software companies retain GUID information about Internet users, for reasons that have not been disclosed.