Ever read service agreements? Neither do I. You might want to take a look at Microsoft’s for Windows 10 though because agreeing to all the terms allows them to poke through the data of your machine. Buried within the gargantuan 12,000 word service agreement it states:
We will access, disclose and preserve personal data, including your content (such as the content of your emails, other private communications or files in private folders), when we have a good faith belief that doing so is necessary to.
Thankfully you can opt out of that, but keep in mind that the default of this feature is ON. Change this by going into Settings and Privacy applet. You should really weed through all the tabs as they state what types of data each app on the system can access.
Additionally, there’s Cortana. It has access to your camera, microphone, contacts, calendar, and probably all your documents. You can turn this off in the Speech applet. You must also create a Microsoft account in order to use many services such as Skype, which is probably just another way for Microsoft to get their hands on your information.
Lastly, Wi-Fi sharing defaults to ON. If you don’t want to be sharing your Wi-Fi with your neighbors better turn this one off too.