HRESULT CoCreateGuid(
GUID * pguid
);
DECLARE INTEGER CoCreateGuid IN ole32;
STRING @ pguid
pguid [out] Pointer to the requested GUID on return.
Returns S_OK (0) if the GUID has been successfully created.
To a very high degree of certainty, this function returns a unique value – no other invocation, on the same or any other system (networked or not), should return the same value.
Read article GUIDs and UUIDs explained on the BetterExplained.
See also: StringFromGUID2, UuidCreate.