The recent cyber attack on the U.S. military's classified computer network has been traced to a front company run by several former Russian KGB or Federal Security Service spies, FOX News has learned.
The attack led the Pentagon to ban the use of external hardware devices, such as flash drives, because that's how the "worm" got into the classified military network.
FOX News has learned the intrusion was discovered by the U.S. military in Afghanistan -- and that the attack came through the local Internet service provider that the Afghans (under U.S. supervision) contracted out to a front company run by former Russian spies.
"There was a preceding effort in denial of service ... by let us say sympathizers to the Russian side of the dispute. That was a prelude and an adjunct to the military attack where Russian troops entered Georgia," Chertoff said. "I think this is a harbinger of what's to come, the use of cyber attacks -- preparing the battlefield, so to speak."
Russia's Federal Security Service (FSB) has denied any involvement in the recent cyber attack, and some Pentagon officials worry the former Russian spies might actually have been working for some other entity.
Chertoff added the U.S. needs a doctrine to decide when a cyber attack is an act of war -- a view echoed by Deputy Defense Secretary Gordon England.
"We have seen it on a small scale already," England said. "This larger future threat will necessarily require the (Department of Defense) to change its thinking and planning. Much like the first use of gunpowder changed the nature of warfare centuries ago."
Jennifer Griffin currently serves as a national security correspondent for FOX News Channel . She joined FNC in October 1999 as a Jerusalem-based correspondent. You can follow her on Twitter at @JenGriffinFNC.