What is the probability of guessing (matching) a Guid?

Question

Just curious but what is the probability of matching a Guid?

Say a Guid from SQL server: 5AC7E650-CFC3-4534-803C-E7E5BBE29B3D

is it a factorial?: (36*32)! =

Answer 1

It is 1 / (number of unique numbers possible with the given UID length). In the above example we see 16 bytes, or 128 bits. 2^128, so the probability of a match is 1 / 2^128.