"Every piece of hardware in your computer has, for the purpose of NSA forensic analysis, it's own unique UUID that is issued by the main controller chip on a particular piece of hardware. If you send anything over the web, your UUID for at least your network interface controller goes out over the web. This permanently identifies hardware as yours, regardless of what you do to wipe it. Windows checked the UUID's on your hardware, and that is how it knew it was placed in a different completely identical machine."
A universally unique identifier (UUID) is an identifier standard used in software construction.
https://en.wikipedia.org/wiki/Universally_unique_identifier