For a more apt analogy, the human immune system is like an old piece of critical software that society depends on, and H5N1 represents a piece of shellcode that

For a more apt analogy, the human immune system is like an old piece of critical software that society depends on, and H5N1 represents a piece of shellcode that exploits a serious flaw in the system which is currently a 0day. It allows an attacker to remotely disable a large number of machines, err, people. There is currently no patch -- vaccine -- available to fix the hole. The relevant buzzword is full disclosure. Even I'm not sure if you can take that so far, but I'm pretty sure that if this is released, nobody ever gets to complain about someone publishing an exploit for their personal project, because that's nothing in comparison.