The online world had joined traditional warfare as the next battlefield, the former CIA counter-terror head during the September 11 attacks told the Black Hat gathering of hackers.
"Now it's your turn," Cofer Black, who now chairs Total Intelligence Services, a subsidiary of private military firm Blackwater Worldwide, told conference delegates in Las Vegas.
"Things have changed."
He said last year's Stuxnet worm attacks on Iran's nuclear power plant computer systems - suspected to have been waged by Israel and the US - were a "huge" validation of this view.
But similar to the run-up to September 11, even though the agency knew of the possibility of an Al-Qaeda strike not everyone appreciated the warning signs.
"Men's minds have difficulty adapting to things with which they have no experience," Black said.
And once an attack happens, he said chaos and confusion was a "great inhibitor" to the proper response. And many questions remained as to what the response would entail. For example, could a cyberattack be met with a physical reaction?
"This is a very delicate window," he said.