Throughout this course we have studied the use of social networks as it relates to several different applications. The above article talks about the use of social networks to combat terrorism.

One key example of the use of social network analysis to understand terrorist cells is the analysis of the September 11^th hijackers. Valdis Krebs, a consultant in Cleavland who builds social network models, modeled the hijackers’ cell starting with two of the hijackers, Khalid al-Midhar and Nawaf Alhazmi. Using information such as frequent flier miles, common addresses, and telephone numbers, Krebs collected a list of interconnections between the terrorists. All nineteen terrorists who carried out the September 11^th attacks were linked by only a few links. Even more interestingly, there were a disproportional number of links to Muhammad Atta, the leader of the September 11^th attacks.

The reason network theory is so useful in combating terrorists is that the National Security Agency (NSA) receives a massive volume of information every day. In order to sort through the 650 million communications that the NSA intercepts daily, a strategy must be developed to decide which communications are more important and which are less important. To do this, the NSA still relies on some information that must be manually selected first, such as the name of a suspect. Starting with the suspect, the NSA builds a network based on connections he has with other individuals and then the list builds out based on the communications of all of the people already identified by the algorithm.