Last Friday, a hacker group called DarkSide deployed a ransomware attack on a pipeline system that carries nearly half of the U.S. east coast's fuel supply. Its operator, the private company Colonial Pipeline, then took the system offline in response to the virtual intrusion. Colonial Pipeline restarted operations on Wednesday evening as panic-induced gas shortages swept across the East Coast and Gulf coast states. The White House said it's closely watching supply shortages. How did the pipeline attack unfold? What does it say about national security cyber-vulnerabilities for all countries?