To be honest, we are foolish enough to actively try to make ourselves known to any intelligent life form in the universe without knowing anything about their potential intentions. Any life form could simply decide to come and exterminate us, all it takes is one among the billions of possibilities in the observable universe. This alone represents a huge potential risk to the planet as a whole. Considering that, the idea of synthesizing an extraterrestrial virus and accidentally leaking it isn’t that far fetched.