Start button > search box, type device manager > Enter > scroll to Image Devices and expand it ( click the pointer in front of )>
Right click at your webcam > at the popup box, click Disable > exit Device Manager.
I disabled mine from startup using Autoruns, which allows me to use it whenever I wish. I then placed a piece of black electrical tape over the webcam lens. I take it as a given that our government has a back door to all software and that they can monitor me at any time they wish but I refuse to give anyone unauthorized access to my webcam, including websites.