Apparently, hackers (or worse, government) can access your webcam without the notification LED switching on. The dutch ministry advised users to put a piece of tape on your webcam when not using it. But that's a sticky situation.. Some companies are now making their own removable "webcam privacy tools".
But why spend money on something when you already have the tools? For most laptops a clothes pin will work perfectly. Just place it over the little webcam lens and voila, no more sneaky peeking. And as an added bonus, you can use it to place your glasses or hang your earbuds!