Or, if you know your netbook very well, you can simply open it up and remove the webcam entirely.
FWIW, most if not all webcams have a little LED next to them. Watch that LED -- you're only in trouble when it's on

It's worth noting, at least for the record, that this is quite likely tinfoil hat territory -- I have a netbook myself, I've had it since 2009, and the only times the webcam has ever been in use, for sure, is when I've accidentally triggered it. I have no use for it, but once in a while in XP I'd hit the wrong button and have to turn it off again. Nobody has ever remotely triggered that webcam, and I rather suspect that nobody ever will.