I have heard that hackers have been able to turn the built-in webcams in computers on from locations long distances from where the computer is located and watch people. I think it's odd people didn't realize the webcam was on because a light should light up if it's working.
I guess sometimes people who don't understand computers very well don't always realize what it means when that light is on. Young children especially, might now question it or think to tell someone about the light being on.
There was a big blowup about this a few years ago when a school made computers available to their students to take home (like borrowing a library book).
To keep tabs on where the computers were. the webcam was engaged by someone at the school. Some students didn't close the lap tops when not in use and so the camera was able to 'view' things going on in the room without consent of the inhabitants of that room. I never heard how this issue was resolved.
Anyway, I covered the camera eye on my laptop with a piece of blue sticky note right after I got the computer since I have no plans to use it, and the sticky note has stayed in place with no trouble. So if anyone turns my camera on they will see nothing but blue skies . . .