My laptop (Acer 5742) has a built-in webcam, however unlike my last laptop there is no operation LED and way of knowing if it is on or not. Just in case someone did get into my system from outside and manage to switch on the webcam, I have constructed a tertiary level of protection just by using a piece of black tape.
Get a length of tape 2 inches long, fold one third over itself, stick side to sticky side. Then mount it on the laptops webcam.
If you ever need to use the webcam, just fold the cover back.