Just a few words on what private data Windows 10 by default allow itself to send to Microsoft:
System Information
- unique advertising ID (shared with 3rd party to track the user)
- unique UUID (e.g. used by NSA to track and attack devices)
- system configuration
- programs crashes
- all installed programs
Users Data
- emails, text messages (e.g. Skype)
- video and audio chat (e.g. Skype)
- contacts from the address book (address, email, phone, etc.)
- precise location (Wifi, GPS)
- Bitlocker recovery keys (these keys decrypt encrypted data, so Bitlocker encryption is pointless)
Users Interest and Behavior
- full browsing history
- app interactions (e.g. a weather app sends locations often requested)
- usage time and frequency of programs
- typing input and behavior
- search requests
Microsoft even admits that the collected data can be tied to the unique user. As all big companies (e.g. Microsoft) have to share data with security authorities (e.g. NSA, GCHQ) on request and furthermore freely share huge amounts of user data, it is safe to say that every piece of data Microsoft has is available to e.g. the NSA as well. Meanwhile the NSA steadily exchanges their information with other agencies around the world. Furthermore most companies sell user data to tracking and advertisement firms.
It is not possible to hinder Windows 10 from leaking all the mentioned data. Finding and using the offered options to minimize the amounts of shared information is difficult and time consuming even for experienced users. On top of that, the majority of user-made changes towards privacy is reverted with every Windows update.
Sources:
Betriebssysteme: Windows
Windows 10’s privacy policy is the new normal | Ars Technica
Even when told not to, Windows 10 just can’t stop talking to Microsoft | Ars Technica
What Data Does Windows 10 Send to Microsoft? Techquickie - YouTube