With the advent of advanced micromechanical
fabrication technology, the spectre of true nanotech
weaponry is rearing its ugly head
Almost everyone in advanced tech is familiar with the concept of grey goo, nanotech self-assembling machinery gone wild. However, it may not be too far-fetched a concept to picture controlled versions of this being unleashed upon enemies to destroy infrastructure and resources.
Other variations of nanotech weapons could also include things like "skin", a concept introduced in the Sci-Fi cable series Odyssey 5. That particularly nasty application was made up of a mass of nanobots which formed a skin covering over a victim, controlling him or her via electrical impulses to the muscles. The drawback was that the "skin" smothered the victim quickly, forcing it to constantly find new hosts.
That corresponds closely with a similar concept I've played with called "puppet dust". If you could get your victim to inhale a quantity of nanobots, they could enter the brain and override the victim's own nerve impulses, taking over the victim and turning them into essentially a remote-controlled zombie.
On a simpler level, they could just enter the body and proceed to destroy everything they came in touch with, kind of an electronic phage.
As micro- and nano-technology improve, these concepts will become more and more feasible, demanding that we address methods of defense and control.