The Gray Goo Scenario
Nanotechnology is an area of science and engineering that involves the study and manipulation of particles 1-100 nanometers in size. They have the potential to bring huge benefits in fields such as science, engineering, computing and, especially, medicine.
The Gray Goo scenario is the possibility that these tiny, self-replicating machines may get out of control and start converting all organic matter on earth into other nanobots. Leaving behind a gray goo and a lifeless earth.
While this may seem to some like nothing more than a science fiction fantasy, the scenario has been taken seriously enough for a top nanotechnology researcher to suggest some public policy recommendations to prevent this from becoming a horrific reality.