Webcam hack?

Hallo,

recently I played a videogame, when I all of a sudden see, that the green light of my macbooks webcam is on and I hear strangers talking in what I guess was french throught the speakers. After 15 min or so it stopped. I did not use skype or any other messenger and did not turn on the webcam. I am using Sophos and the firewall feature from my macbook was activated. Does anyone have a clue what was going on on my mac???