What is a GUID?

GUID stands for Globally unique identifiers.  When an ActiveX control is registered, it writes a global identifier in the registry .  When your program looks for an active X control it is actually looking for an ActiveX control with a certain GUID.  When new functionality to add to a component, such as a new event method or property is added, the component receives a new GUID ( and a full version upgrade, for example: version 2 to version 3).