So far, said Richard Clarke, head of the White House's Office of Cyberdefences, al-Qaeda and other terrorist organisations have limited their use of the Internet to communication and propaganda purposes.
"None of those traditional terrorist groups has yet to attack over the Internet," said Clarke, who appeared yesterday (13 February before the US Senate Judiciary Subcommittee on Administrative Oversight and the Courts, but "that may be about to change".
There is now evidence found in caves in Afghanistan, said Clarke, that al-Qaeda "was using the Internet to do at least reconnaissance of American utilities and American facilities".
Clarke said al-Qaeda was gathering useful information off public Web sites. "If you put all the unclassified information together, sometimes it adds up to something that ought to be classified," he said.
Clarke said the US does not know whether there have been successful penetrations of critical infrastructure networks. But, "if I were a betting person, I would bet that many of our key networks have already been penetrated," he said.
Trap doors, a secret means to gain network access, and logic bombs, devices that can cause systems havoc when triggered, "may already be in many of our key infrastructures because it is easy to do," said Clarke.
Committee Chairman Charles Schumer warned that a "well-planned and well-executed cyberattack on America wouldn't just mean the temporary loss of e-mail and instant messaging. Terrorists could gain access to the digital controls for the nation's utilities, power grids, air traffic control systems and nuclear power plants".
The threat isn't just from terrorists groups. Criminal organisations, teenage hackers and nations such as Iraq, Iran, China, North Korea and Russia have all developed information warfare units, said Clarke.
However, Clarke added, US software makers such as Microsoft are taking steps to improve the security of products. That effort is coming partly in response to Sept. 11, but also to some virulent viruses that have caused $12bn (£8.4bn) in damages last year.
That damage caused a lot of end users to ask vendors why companies were paying so much for products that aren't secure. "I think the word has gotten through to the IT manufacturers," he said.
Clarke said the US doesn't know the capability of potential enemy countries or terrorists groups to conduct cyberwarfare. Unlike physical weapons, he noted, "There's nothing for our satellites to take pictures of."