Sam is a smart guy, so I really don't want to come off as sounding like a jerk here, but this grossly underestimates the technical feasibility of creating such a virus. Computer folks routinely overestimate how much biologists actually know about the systems we study. We know jack about how the vast majority of biology works. We have the most fleeting glimpses of understanding that are regularly crushed by the complexity of dynamic systems with nested feedback loops and multiple semi-overlapping redundancies. I won't say it's impossible, but we don't even know enough to know whether the three things: high mortality, long incubation, and ease of transmission are even possible. While we can imagine it, there might be biological and epidemiological factors that prevent such a thing from existing.
This also commits the logical fallacy of ascribing superpowers to the bad guys cooking up viruses while assuming the good guys are sitting on their duffs letting bad things happen. H5N1 was a pretty good example of international collaboration. There were academic competitors and industrial labs working around the clock collaboratively on it in the early days before much was known. Whole vaccine divisions at pharmas were all over it. If we're instead talking about a mythical time in the future when we do understand enough biology to engineer something like this, one would have to assume the good guys possess the knowledge to develop countermeasures.
I'm not arguing that pandemics aren't something we should worry about. Europeans were almost wiped out by the plague and in modern times Africa has been decimated by HIV. These are real problems that the human race has faced and will likely face again, irrespective of lab-created stuff. Biotechnology is the primary mechanism by which we're going to be able to survive when the next one comes, wherever it comes from.
EDIT: Fixed wrong word usage in 2nd sentence.