Here's a photo of my laptop:
As you can see, I have a piece of paper taped over the built-in camera/webcam. There's a good reason for this. Last year, I had the opportunity to visit a Cybercrime Investigation Unit at a State Police facility. I took part in an informative Homeland Security briefing about the various dangers that exist from hackers who attack computers in the United States.
The briefing was eye-opening and scary. One of the things we talked about was the way that hackers can remotely access the camera on your computer and spy on you without your knowledge. This is not science fiction or a weird rumor: it's a fact.
Here's a link to the Ars Technica website with an article about this disturbing practice, known as "RATing": http://arstechnica.com/tech-policy/2013/03/rat-breeders-meet-the-men-who-spy-on-women-through-their-webcams/
The investigators I met advised that if you have a camera built in on your laptop or tablet, take immediate steps to disable it, and make sure you keep your computer's firewall secure at all times. Check frequently for updates, and run anti-virus software automatically.
If you need a quick, low-tech solution, you can do what I did: grab a piece of tape and a scrap of paper and stop these criminals from invading your privacy!