blur traditional security borders. While this increased reliance on interlinked capabilities helps make the economy and nation more efficient and perhaps stronger, it also makes the country more vulnerable to disruption and attack. This interdependent and interrelated infrastructure is more vulnerable to physical and cyber disruptions because it has become a complex system with single points of failure. In the past an incident that would have been an isolated failure can now cause widespread disruption because of cascading effects. As an example, capabilities within the information and communication sector have enabled the United States to reshape its government and business processes, while becoming increasingly software driven. One catastrophic failure in this sector now has the potential to bring down multiple systems including air traffic control, emergency services, banking, trains, electrical power, and dam control. The elements of the infrastructure themselves are also considered possible targets of terrorism. Traditionally, critical infrastructure elements have been lucrative targets for anyone wanting to attack another country. Now, because the infrastructure has become a national lifeline, terrorists can achieve high economic and political value by attacking elements of it. Disrupting or even disabling the infrastructure may reduce the ability to defend the nation, erode public confidence in critical services, and reduce economic strength. Additionally, well chosen terrorist attacks can become easier and less costly than traditional warfare because of the interdependence of infrastructure elements. These infrastructure elements can become easier targets where there is a low probability of detection. The elements of the infrastructure are also increasingly vulnerable to a dangerous mix of traditional and nontraditional types of threats. Traditional and non-traditional threats include equipment failures, human error, weather and natural causes, physical attacks, and cyber attacks. For each of these threats, the cascading effect caused by single points of failure has the potential to pose dire and far-reaching consequences. Challenges There are fears that the frequency and severity of critical infrastructure incidents will increase in the future. Although efforts are under way, there is no unified national capability to protect the interrelated aspects of the country's infrastructure. One reason for this is that a good understanding of the inter-relationships does not exist. There is also no consensus on how the elements of the infrastructure mesh together, or how each element functions and affects the others. Securing national infrastructure depends on understanding the relationships among its elements. Thus when one sector scheduled a three-week drill