Could terrorists, intent on causing as much harm and societal disruption as possible, use new biotechnology processes to engineer a virulent pathogen that, when unleashed, would result in massive numbers of dead? Mark Williams, in his article "The Knowledge," suggests we should be contemplating this doomsday scenario in the 21st century. Williams's article might make you sleep less soundly, but are the threats real? The truth is that we do not really know.

Part of the problem is that even if terrorists could create new pathogens virulent to humans, it's not at all clear that they could "weaponize" them -- that is, put the pathogens into a form that is highly infectious to humans and then disperse them in ways that expose large numbers of people.