Can someone view my webcam without my permission?
Assuming you have set your cam for permission-based viewing the answer is basically no. Using a Cam-Viewer type program has never been proven to actually let you break into someones webcam without their knowledge and is extremely unlikely. Most of these so-called Cam-Viewer programs only allow the user to remain anonymous - you still get a request from Yahoo for "anonymous" to view your webcam. The only real way a user may be able to view your cam without your knowledge is if your system has been compromised by a backdoor trojan. It's very easy to trick someone who isn't very computer literate into accepting such programs and there are a ton of them. If one is installed on your computer, the person could easily know exactly what programs you are running (such as Yahoo Messenger) and could even take control of the webcam and send the photos to his/her self. If you do suspect someone has this ability, run an up-to-date virus scan, and perhaps even
search for a trojan scanner for a more thorough analysis.