Spy Hunter is a security app for Windows Phone 8 that will help you catch those who like to spy on your phone while you are not around.
Once the trap is set, Spy Hunter snap a series of photos of the culprit, sounds an alarm and will record audio when your Windows Phone is unlocked. You also have the options to automatically save your photos to SkyDrive and receive notifications when Spy Hunter is triggered.
Spy Hunter has a friendly user interface and not a bad option to consider if you need to find out who keeps messing with your Windows Phone. However, it is not exactly fool proof.