It is an interesting risk assessment worrying about engineered viruses, when we are literally surrounded by them and any of them could mutate and become dangerous. I have always assumed that an engineered virus specifically engineered to not transcend its limits would be less likely to become a problem than all the other viruses whose ability to mutate around our immune systems is required for them to survive more than a few years. Or is there a factor I'm unaware of, such as the the most useful sources to work from are also the most virulent with nasty behavior just one mutation away from being switched on?