Biological Weapons
Biological weapons can be a missiles or mortars capable of carrying and delivering their contents effectively. In this case the contents can be a virus, a type of bacteria or a deadly fungus. Genetic engineering is used to change the virus or bacterium making it impossible for an opposing nation to prepare a cure for it in advance. The virus or bacterium can also mutate making it even more difficult to find a cure and eradicate it. The danger of this weapon is very real, but it will never be used on a large scale not even by terrorists. This is because viruses and bacteria tend to spread quickly and are hard to control. When released an outbreak of the virus or bacteria can spread globally and thus also effecting the terrorist who released it in the first place. The more the times passes the more it has a chance to mutate, making it harder and harder to stop.