I am afraid that my webcam was hacked (

Hello. I had a strange situation this evening. I was scrolling pictures in the Preview app in the fullscreen mode, then paused for a minute or two, and a strange white flash (blink) happened on my screen, like one you get when using photobooth shot. I wanted to check if its similar and opened photobooth. App said that is no camera connected. I selected Camera option in the top menu, built-in camera was here but it was grey and has (in use) in the label. Maybe not 'in use', its my translation because my language is not English but the meaning was clearly the same. I checked if any apps were using camera but found none. I rebooted my macbook and photobooth started to work again. This situation made me feel nervous and I came here. Specs are Macbook pro mid 2012 13", High Sierra. Thanks in advance.