Sometimes I think that people really don't understand that something similar to a zombie outbreak can actually happen. If some terrorist organization or government planned it, they could do it if done intelligently. The outbreak would have to start in dozens or hundreds of locations at the same time, but it could be done. All that they'd need to do is modify rabies a bit, or add a lil somethin'. Then BAM, we got a flesh-eating zombie. It will not be a global catastrophe if it isn't a coordinated attack, as it will take time for each infected to show symptoms of the virus (e.g. rage, hunger, etc). However, this is something that could be done. It may not destroy the world, but it could do some damage.
You good.