Posted this in chat and don't know how to move it? So I have just reposted here - sorry if this is against rules or something.
Have a MacBook Air. Noticed the green webcam light was on, but I wasn't using the camera and haven't used FaceTime/iPhoto etc since I got it last year - haven't used camera at all really.
I google and there were a couple of people on Apple threads with a similar problem... and some things did come up about poss. of people watching you on the camera?
So, I decided to cover the camera with blue-tack. Took it off after 5mins and light was still on so put it back on. Waited another 5mins and light had turned off.
So, am I being completely paranoid to think that someone else could have been accessing my webcam? No idea how long it was on for until I saw it, but I've been on it since about 4pm working. Does anyone it's possible or is there a more likely explanation? 
Thanks.