Historically when a country has been attacked deciding whether or not to declare war or how to properly respond has been a relatively straight-forward task.

Pearl Harbor bombed, declare war; merchant ships targeted by U-Boats, declare war; German tanks roll over your border, declare war. Jump to the 21st Century with warfare being waged over fiber optic cables and deciding whether a cyberattack is an act of war, a crime or just online vandalism is a much more difficult and complex task that our nation’s decision makers are just starting to contemplate. And even when the attack has been properly defined, deciding upon a proportional response is no easy matter.

Source: Senate bill asks Obama administration to define cyber war