Certainly impossible to rule out at this point.
I just think that if they release ANY serious virus, their pride will be their downfall, at least for some of them. They might THINK they have it figured out (antidotes, vaccines, etc.) but something always goes wrong. It's dangerous to unleash a monster that YOU YOURSELF are vulnerable to. Just watch any movie.
Remember Jurassic Park? The fat programmer made the electric fences go down so he could escape with the DNA samples, but what happened? He ended up getting eaten by a carnivorous dinosaur -- partly because of his own evil actions. That part of the movie was good because it was SO REALISTIC you could just imagine that happening in real life.
Two words: MURPHY'S LAW.
I know it's not an actual law, but it sure seems to be true. Otherwise, why does the phrase "Murphy's Law" have such legs -- such popularity? It's been around for how many decades, going on a hundred+ years? If there were no truth in it, the saying would have died LONG ago.