With the Windows 10 anniversary update Cortana, the voice assistant, is enabled by default.  It can be asked questions and accessed even if  your device is locked leaving it vulnerable to hackers. This was brought to everyone’s attention when researchers were messing around and discovered they could get Cortana to visit a malicious website just by asking regardless of whether the screen was locked or not.  If you don’t use Cortana, this isn’t an issue. However if you do use it, you can change its settings to turn off when the screen is locked.  Check out this How-To_Geek article to find out how.