All sarcasm aside, there is nothing to worry about. There isn't anything interesting to see from the viewpoint of the webcam, and it is by far the least accessible way to monitor someone on a computer. Plus you are using a mac, so the chance of getting malware, especially something that nasty is basically zero. If you are still too worried, don't use the internet. You can't use it without a keyboard, which, even though the chances are almost zero, can be monitored, giving much more information than the iSight. Basically, don't worry about it.