When does Cyber Warfare become Warfare?

I think most of us would agree that hackers sponsored, aided, or working directly for a foreign government hacking into a nuclear power plant and causing a meltdown would fall into the category of "Act of War".

What about disabling the power grid, say a week or two long outage in the northeast? Causing a commuter train crash or airplane crash?  

How about hacking into the White House? 

What constitutes cyber warfare and when does it cross the line into warranting a "kinetic" response.  For those of you unfamiliar with the term, a kinetic response is good old fashioned warfare, i.e. blowing shit up.

One could launch a missile from a submarine off the cost, striking a nuclear plant, breaching containment, and pretty much ruin a good day and we'd all agree that is an act of war.  Is there a difference between blowing up a centrifuge with an iron bomb or causing it to self-destruct with a virus?

Now hacking the White House probably doesn't rise to the level of an act of war, more like the old school espionage days of breaking in and rifling through the desks and file cabinets, but the lines between cyber activities and kinetic activities are blurry and ill defined.  Where do you think they ought to be?

On a lighter note, pictured above is a Control Data Cyber 170 Mainframe, a system I used to work on many years ago.  The woman is changing a multiple platter disk drive, today... the equivalent of those four large disk drives would easily fit unnoticed in your pocket. The guy in the pink shirt is standing before a bank of tape drives and every eight minutes someone had to get up and change a tape... each reel contained over a mile of magnetic tape.