There are lots of ways that an intruder can do nefarious things, including but not limited to making the magic smoke come out of things, creating a network over an air gap, downloading firmware to the webcam so that it can be turned on without the LED lighting up and so on.

Many people used to think that those of us who came up with seemingly theoretical scenarios were just paranoid, but thanks to the true American hero, Edward Snowden, we know they're not only worth worrying about but they're actually used in real life. We should ALWAYS be wary of who and what we trust.