In "Cyber War!" FRONTLINE investigates a number of cyber attacks that have already occurred in recent years, including "Slammer," which last January took down the Internet in South Korea and affected 911 systems and the banking system in the United States, and the "Nimda" virus that quietly attacked Wall Street in 2001.
FRONTLINE talks to cyber security experts about what these defining wake-up calls reveal about the vulnerabilities of cyberspace. This report also follows efforts by the United States to go on the offensive.
"You cannot defend yourself unless you understand how the offense works. And in so doing, you learn to wage offensives," says John Arquilla, associate professor of defense analysis at the Naval Postgraduate School in Monterey, Calif. Arquilla has helped the Department of Defense develop information warfare strategies utilized in the first Gulf War, Kosovo, Afghanistan, and in the most recent war with Iraq.
But many cyber war experts believe the Internet could be used to launch a major attack on the nation's infrastructure.
"What we found on Al Qaeda computers was that members of Al Qaeda were from outside the United States doing reconnaissance in the United States on our critical infrastructure," says Clarke.