Each object that is exposed for creation must have a unique CLSID. CLSIDs are universally unique identifiers (UUIDs, also called globally unique identifiers, or GUIDs) that identify class objects to OLE. The CLSID is included in an application, and must be registered with the operating system when an application is installed.
To generate UUIDs, run the Guidgen.exe utility. By default, Guidgen.exe puts a DEFINE_GUID macro on the Windows Clipboard, which can then be pasted into your source code.