This was a bigger story a few years back, but it's still very applicable.
People buy Web cams that will allow them to put them on the Web. As with many computer issues, people want ease of use and ignore security.
On the second page of this article (click "Continue"), Scott Bradner shows you some of the Google search strings that can show Web cams. Some are surely left public for a reason...but others just show stuff you'd assume people didn't intend to leave public.