These then arrange themselves in a completely random order, which is mathematically so difficult to replicate it's known as PUF (physically unclonablefunction).
ENGADGET: IBM brings the fight to counterfeiters with nano-sized authentication methods (video)
2.
This fingerprint (aka PhysicallyUnclonableFunction, or PUF) is a byproduct of tiny errors in the fabrication process -- something chip makers usually try to minimize.