But there may never be a clear answer on when to fire back against a computer-based attack, said James Miller, the principal deputy undersecretary of defense at a Washington conference.

The Pentagon has been working through a range of scenarios, in an effort to come up with rules of war that will work in an attack that can be launched from continents away in milliseconds, and routed through innocent civilians' computers by unknown assailants, according to The Guardian.

Miller said there is unlikely to ever be a single answer, and officials may just have to use their judgment because of all the grey areas in this field.

The US has set up a new military command for cyber warfare capable of both offensive and defensive operations as part of a national strategy to secure US digital networks.

Miller said the new organization, which is expected to be fully operational in October, will have a number of challenges, including determining what kind of cyber attack will constitute an act of war.

This article was first published by Computer Weekly