Scientists have created it in order to protect against it. Few people today know about the flu pandemic of 1918, but it killed more people than World War I. And, unlike most influenza, it mainly killed people who were in their 20s or 30s… people who should have been the healthiest.
It was fear of another such influenza strain which led to the world wide global monitoring of flu, and the creation of an annual flu vaccine. The vaccine needs to be annual because influenza mutates at a high rate. This is why a new shot is needed every year… the newer strains circulating in the world are not protected against by the older vaccinations.
The possibility of biological warfare is real, even if the track record of using microorganisms for that purpose is non-existent. The tools for creating new strains of influenza (or other infectious agents) have been around for some time now. And it is possible that a rogue state could misuse them. I think its a good idea if we know how to protect ourselves. And in order to do this, we need to understand the possibilities which might occur.