It's been argued that a GUID doesn't do a good job of being a one time security token , and it makes sense because GUIDs aren't random.
In my scenario: suppose a given company is using GUIDs as a security token, and needs to see the math behind the possibility of a security breach, before they will consider it a security concern...
That being said:
What is the statistical probability of an outsider guessing a GUID?
From what I can tell, the probability increases if the attacker knows the time/date the GUID was generated; but I don't know how to calculate the degree / scope of the vulnerability.
The probability also increases if the GUID is generated on the same machine (and perhaps the attacker knows this) for GUID versions 1 though 3. I'm unsure if this also applies to GUID version 4.