David Hoffman sets the scene:
What would a president of the United States say to the country if thousands of people were dying from a disease or trapped in a massive blackout and he did not know who caused it? A ballistic missile leaves a trajectory that can indicate its origins. An airline hijacker might be caught on video or leave behind a ticket or other telltale clue to his identity. When someone is shot with a weapon, the bullet and firearm can be traced. Not so for many cyber and bio threats.
Michael Joseph Gross has a full profile of the Stuxnet worm:
Because cyber-weapons pose an almost unsolvable problem of sourcing--who pulled the trigger?--war could evolve into something more and more like terror. Cyber-conflict makes military action more like a never-ending game of uncle, where the fingers of weaker nations are perpetually bent back. The wars would often be secret, waged by members of anonymous, elite brain trusts, none of whom would ever have to look an enemy in the eye. For people whose lives are connected to the targets, the results could be as catastrophic as a bombing raid, but would be even more disorienting. People would suffer, but would never be certain whom to blame.
Stuxnet is the Hiroshima of cyber-war. That is its true significance, and all the speculation about its target and its source should not blind us to that larger reality. We have crossed a threshold, and there is no turning back.