Microsoft has confirmed that Windows includes a Global Device ID (GDID), a unique, permanent identifier linked to each device and user, which cannot be turned off. This identifier allows #Microsoft to track user activities across its services. The existence of the GDID became public after it helped authorities identify a suspect linked to a hacking group. The ID is stored in the Windows registry and remains even after updates but changes with a full reinstallation.

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Microsoft Confirms Windows Has a Global Device ID You Can't Turn Off

It's designed to manage software licensing, but Microsoft can also use it to identify individual users.

^{Jon Martindale (Yahoo Tech)}