Can someone hack into your webcam and watch you when your using it?

Ok. Gonna cut right to the chase. In the past when my girlfriend and I (who live in different states when we are not at college) had gone a long while without seeing eachother, we got into the habit of getting naughty on our webcams occasionally when we did video chats. Then she heard from someone that it is possible to hack into a webcam and watch a video that was meant to be between the two of us. Is this possible, and if so, how high is the risk? Should I be worried that I have unintentionally released nude images of my girlfriend and I onto the web? Please help.

It should also be known that neither of us used our webcams for anything except for talking to eachother. I thought that that meant we were safe. Is that a safe assumption?

Unfortunately, nothing is impossible, but you probably have better chances of getting hit by a car.

Keeping both PCs clean of any malware and viruses should be more than enough.