Microsoft has a Global Device Identifier (GDID) that tracks Windows devices, which was used by the FBI to catch a hacker. The GDID is a unique identifier assigned to a Windows device when a user signs into a Microsoft account, and it can be used to track a device's activity across the internet. The identifier is not reset when a user reinstalls Windows, but a new one is generated. The use of GDID has raised concerns about user privacy and surveillance.