How is it that my OS says that the webcam app needs to quit, when I did not turn it on in the first place?

Sometimes when I am turning off my laptop there is a message that an application is open and needs to terminate. This application is my webcam. I am worried why this happens since I am not using my webcam (and not using programs that use my webcam). I am worried that someone hacked it. Could you give me some ideas why that happens and what can I do about it?