Cyberwarfare: The most dangerous kind might not even require a PC

The real trick, of course, is to cut the right cables.

The Internet is a graph with many interconnected nodes, and when one node fails traffic is routed through other nodes. If you cut out the right nodes the resulting traffic will overload the nodes that the traffic is redirected to, causing them to fail too, and in turn rerouting to other nodes that will also fail under the increasing load. A cascading failure.

I remember reading a report where someone calculated that if the right three major routers in the US were taken out the entire Internet would grind to a halt within minutes. This could probably also be achieved by cutting the right cables.

The real danger is terrorists with shovels that know their graph theory.

Extrapolating further, once computerized implantable medical devices and/or nanotechnology become more prevalent, his general point will be even scarier.

The "most dangerous kind" is just regular warfare, i.e. physically disrupting infrastructure.