Taking down the internet: possible but how probable?

The hack of the Democratic National Committee this past summer, allegedly by Russia, prompted a political firestorm, but didn’t cause even a ripple in the US economy.
But imagine the economic firestorm that would result if online attackers brought the entire internet down, even temporarily.
You may not have to imagine it, according to Bruce Schneier, CTO of Resilient Systems, cryptography guru, blogger and international authority on internet security. In a recent post titled, "Someon