I don't know if there's a name for it, but this is kind of like "security by obscurity". I'm not sure I would just make the assumption that there's no possible way a terrorist group can engineer a virus capable of killing half the world's population and call it good. For example, it's entirely possible that the terrorist organization could kidnap researchers and force them to do it.

If kidnapping researchers and forcing them to do it is an issue, why wouldn't they just kidnap the people who did this study?

We aren't talking about a bond villain, here. We're talking about largely uneducated Arab peasants who are perfectly capable of firing an RPG-7 or an AK-47, or strapping on an explosive vest and blowing themselves up, but little else. There's no evidence they're even making their own PETN, which is far easier than engineering a virus. In fact, instructions for the manufacture of PETN, and the constituent components thereof, are freely available.

The rush to ascribe fantastical abilities to terrorists has led to the introduction of some pretty draconian laws. Given that bathtubs kill more Americans than do terrorists, let's lay of the doomsdaying, shall we?