A GUID is theoretically non-unique. Here's your proof:
- GUID is a 128 bit number
- You cannot generate 2^128 + 1 or more GUIDs without re-using old GUIDs
However, if the entire power output of the sun was directed at performing this task, it would go cold long before it finished.
GUIDs can be generated using a number of different tactics, some of which take special measures to guarantee that a given machine will not generate the same GUID twice. Finding collisions in a particular algorithm would show that your particular method for generating GUIDs is bad, but would not prove anything about GUIDs in general.
