Scientists at defence research organisations are currently working on understanding the impact of nanotechnology in military applications. Whilst most of this site has looked at the positive benefits Nanotechnology can bring, this research is being looked at to be used in the creation of weapons of mass destruction that could, potentially, be more dangerous than nuclear weapons and have a huge effect on our lives and the world's ecosystem.
The militaries of many countries worldwide now have weapons using nanotechnology advancements. The use of them can be classified in four ways:

Damage to The Lungs
Mainly due to their size, nano particles can easily get deep inside the lungs to cause damage. Already ultra fine particles from items such as diesel machines and power plants can cause significant damage to human lungs. With nanoparticles, other chemicals could be taken inside the lungs to cause damage to the human body from the inside.

Other Entry Methods
Nano particles can also get into the body through the skin, eyes, ears and digestive system. This could then cause cell damage by creating free radicals. Also, as the nano particles could easily get inside the bloodstream, it is feared that they can cross the blood brain barrier and cause serious problems.

No Natural Immunity
Although the human body has developed a tolerance to natural elements, nano particles aren't natural. Therefore the body has no immunity to them so is more likely to find them toxic and suffer from them.

Nano Bomb
This is the most dangerous weapon created by nanotechnology for military purpose. It contains engineered deadly viruses that can self multiply in order to wipe out its intended target - however big. This is the use of nanotechnology which many peolpe have come to fear.

Militaries are about to embark on a war of nano-weapon advancements, using which huge armies could be wiped out without fighting a single battle and without knowing what had happened.