I know not with what weapons the first world cyberwar will be fought, but I know the second will be fought with floppy disks.

Why do you think that different countries have put missiles in submarines ?

And Russia reportedly even has a deadmans-switch that can be triggered by seismic activity on Russian soil and rapid changes in air pressure. I'd presume that such a system is not connected to the internet.

All of those systems predate the Internet, so you bet nuclear capabilities will not be affected much by cyber attacks.

Nuclear capabilities will probably not be affected much by cyber attacks over the internet. There are other vectors, but they obviously require a much more serious investment in espionage, spycraft, etc.

Isn't this literally the denoument of Dr Strangelove?