Have you considered all your privacy options? Much ado has been made recently about Microsoft arm-wrestling users into upgrading to Windows 10.
Personally, it’s one reason I chose to not enable Cortana Voice. A so-called “truly personal assistant,” except for the fact that my so-called assistant dictates to me.
Even if you have upgraded already, you can still modify your privacy settings.
For the quick and dirty approach, use this.
If you’re truly paranoid and want something more in depth, go here.