It is far, far more easy for a malicious person to intentionally create something "bad" than for a good person to do it by accident. That said, a malicious per

It is far, far more easy for a malicious person to intentionally create something "bad" than for a good person to do it by accident. That said, a malicious person would not be able to create something "bad" without a tremendously large amount of funding and manpower. So lets imagine a malicious person with funding and manpower turns up: Sure, totally synthesised genomes will turn up and you will be able to email some guy who generates your operon to stick into whatever, so the barriers of entry for a bio-terrorist will be lowered somewhat; but even then the knowledge of how to create a killer virus will be scarce. And after 20+ years of gained knowledge, once a billionaire Bond-villain with a fortress of henchmen* has made a killer virus, it is tricky to imagine it out-competing any virus created by nature's hands - she had several million years worth of head-start and a hell of a lot more funding. So, yes, it is very unlikely, but still possible. However, if you were going to go to all that work to spread some virus, I would strongly recommend that you just learn to make nukes instead. They are much more reliable, predictable, and will have less fallout for you to worry about. *Although a Government could much more probably fill this role.