Fears that services like fire brigade could be at risk
Computer experts have painted a chilling picture of the potential threat from a combined terror and cyber-attack on the United States.
They told Congress that terrorists could target computer networks critical to power supplies, telecommunications and financial systems and wreak havoc on the country.
Fears of a cyber-assault on the US have been heightened following the 11 September attacks.
President Bush has already moved to head off any danger by appointing a computer security veteran as special White House advisor for cyberspace security.
'Beyond frightening'
Speaking before the House Science Committee, computer security expert Terry Benzel said the potential for an attack on America's computer networks was "beyond frightening".
"What if the attackers were able to compromise systems monitoring the water supply for Manhattan? What if power to parts of the northeast corridor could have been brought down through a cyber-attack on key systems?
"We must prepare now to prevent this from happening," she urged.
Her fears were echoed by committee chairman Sherwood Boehlert. He warned that research and development on computer security had not kept pace with the threat.
"To put it simply, we need more people to be doing more creative thinking about computer security. That's what our adversaries are doing," he said.
Vulnerable networks
An official report released the day after the September attacks highlighted the vulnerability of America's computer networks.
"Recent reports and events indicate that these efforts are not keeping pace with the growing threats and that critical operations and assets continue to be highly vulnerable to computer-based attacks," said the US Government report.
Experts have been warning for some time about what has been described as an Electronic Pearl Harbour - a computer-based attack that would cause massive amounts of destruction and loss of life.
In a worst-case scenario, such an attack would target power distribution, financial services, emergency call services and air traffic control systems.
Shortly after the shocking events of 11 September, an influential US thinktank warned that cyber-attacks could become part of any future conflict.
'Nuisance attacks'
"The vast majority of previous politically related cyber-attacks have been nuisance attacks, and it is extremely likely that such attacks will follow any US-led military action," said the report by the US-based Institute for Security Technology Studies.
"The potential exists for much more devastating cyber-attacks following any US-led retaliation to the 11 September terrorist attacks on America. Such an attack could significantly debilitate US and allied information networks".
The Bush administration has acted to address the issue with the appointment of Richard Clarke as special White House advisor for cyberspace security.
Mr Clarke has a long record in counter-terrorism and cyber-security, most recently serving as national co-ordinator for security, infrastructure protection and counter-terrorism on the National Security Council.
But some are sceptical about the idea of dramatic assault on computer networks in the US. Computer security expert Richard Forno said cyber-attacks were more of a nuisance than viable terrorist tactics, warning against any knee-jerk measures.