Depending on where you live, using this viewer may be considered illegal for various reasons. However, the viewer itself uses no malicious exploits in order to produce an image. All images are obtained by making a single HTTP GET request to the feed URL, which requires no special browser configuration or authentication to access. Most of the cameras in the viewer were found using Google searches.
When you view webcams using the viewer, your browser is making a direct connection to each webcam over the Internet. All the viewer does is point your browser in the right direction. In short, use this viewer at your own risk.