Not meaning to sound paranoid but windows 10 preview grants too many liberty's for microsoft. I personally will never use it.
 
Essentially they log keystrokes, sound, video (attached cameras ect) any network you connect to, and any privacy solutions you use (vpn tor ect).
 
   Microsoft collects information about you, your devices, applications and networks, and your use of those devices, applications and networks. Examples of data we collect include your name, email address, preferences and interests; browsing, search and file history; phone call and SMS data; device configuration and sensor data; and application usage.
 
   We may collect information about your device and applications and use it for purposes such as determining or improving compatibility" and "use voice input features like speech-to-text, we may collect voice information and use it for purposes such as improving speech processing.
 
   If you open a file, we may collect information about the file, the application used to open the file, and how long it takes any use [of] it for purposes such as improving performance, or [if you] enter text, we may collect typed characters, we may collect typed characters and use them for purposes such as improving autocomplete and spellcheck features.
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