I don't know if this would work for a video, but I think this might work.
How flash player works and why it is so insecure. Why does it have so many security problems when other programs don't. I think it would be an interesting video.
I've been interested in this topic for a while but I can seem to find stuff explaining why its bad. All I find is "flash is bad, uninstall it now!". but I'm lazy so I don't search that far anyways.
Also I'm assuming adobe is competent and the problems with flash isn't an easy fix but an inherent flaw with how flash was originaly built. Which is why I think it would be interesting. But if it is just adobe being incompetent then this post is pointless.
