One of the excellent features of new Windows devices is that disk encryption is built-in and turned on by default, protecting your data in case your device is lost or stolen. But what is less well-known is that, if you are like most users and login to Windows 10 using your Microsoft account, your computer automatically uploaded a copy of your recovery key – which can be used to unlock your encrypted disk – to Microsoft’s servers, probably without your knowledge and without an option to opt-out.
https://theintercept.com/2015/12/28/recently-bought-a-windows-computer-microsoft-probably-has-your-encryption-key/