On Heterogeneous Covert Networks

Covert organizations are constantly faced with a tradeoff between secrecy and operational efficiency. Lindelauf, Borm and Hamers (2008) developed a theoretical framework to deter- mine optimal homogeneous networks taking the above mentioned considerations explicitly into account. In this paper this framework is put to the test by applying it to the 2002 Jemaah Islamiyah Bali bombing. It is found that most aspects of this covert network can be explained by the theoretical framework. Some interactions however provide a higher risk to the network than others. The theoretical framework on covert networks is extended to accommodate for such heterogeneous interactions. Given a network structure the optimal location of one risky interaction is established. It is shown that the pair of individuals in the organization that should conduct the interaction that presents the highest risk to the organization, is the pair that is the least connected to the remainder of the network. Furthermore, optimal networks given a single risky interaction are approximated and compared. When choosing among a path, star and ring graph it is found that for low order graphs the path graph is best. When increasing the order of graphs under consideration a transition occurs such that the star graph becomes best. It is found that the higher the risk a single interaction presents to the covert network the later this transition from path to star graph occurs.covert networks;terrorist networks;heterogeneity;game theory;information;secrecy

Understanding Terrorist Network Topologies and Their Resilience Against Disruption

This article investigates the structural position of covert (terrorist or criminal) networks. Using the secrecy versus information tradeoff characterization of covert networks it is shown that their network structures are generally not small-worlds, in contradistinction to many overt social networks. This finding is backed by empirical evidence concerning Jemaah Islamiyah's Bali bombing and a heroin distribution network in New York. The importance of this finding lies in the strength such a topology provides. Disruption and attack by counterterrorist agencies often focuses on the isolation and capture of highly connected individuals. The remarkable result is that these covert networks are well suited against such targeted attacks as shown by the resilience properties of secrecy versus information balanced networks. This provides an explanation of the survival of global terrorist networks and food for thought on counterterrorism strategy policy.terror networks;terrorist cells;network structure;counterterrorism

The Influence of Secrecy on the Communication Structure of Covert Networks

In order to be able to devise successful strategies for destabilizing terrorist organizations it is vital to recognize and understand their structural properties. This paper deals with the opti- mal communication structure of terrorist organizations when considering the tradeoff between secrecy and operational efficiency. We use elements from game theory and graph theory to determine the `optimal' communication structure a covert network should adopt. Every covert organization faces the constant dilemma of staying secret and ensuring the necessary coordina- tion between its members. For several different secrecy and information scenarios this dilemma is modeled as a game theoretic bargaining problem over the set of connected graphs of given order. Assuming uniform exposure probability of individuals in the network we show that the Nash bargaining solution corresponds to either a network with a central individual (the star graph) or an all-to-all network (the complete graph) depending on the link detection probabil- ity, which is the probability that communication between individuals will be detected. If the probability that an individual is exposed as member of the network depends on the information hierarchy determined by the structure of the graph, the Nash bargaining solution corresponds to cellular-like networks.covert networks;terrorist networks;Nash bargaining;game theory;information;secrecy

One-Mode Projection Analysis and Design of Covert Affiliation Networks

Subject classifications: Terrorism; Counterinsurgency; Intelligence; Defense; Covert networks; Affiliation networks.

Understanding Terrorist Network Topologies and Their Resilience Against Disruption

This article investigates the structural position of covert (terrorist or criminal) networks. Using the secrecy versus information tradeoff characterization of covert networks it is shown that their network structures are generally not small-worlds, in contradistinction to many overt social networks. This finding is backed by empirical evidence concerning Jemaah Islamiyah's Bali bombing and a heroin distribution network in New York. The importance of this finding lies in the strength such a topology provides. Disruption and attack by counterterrorist agencies often focuses on the isolation and capture of highly connected individuals. The remarkable result is that these covert networks are well suited against such targeted attacks as shown by the resilience properties of secrecy versus information balanced networks. This provides an explanation of the survival of global terrorist networks and food for thought on counterterrorism strategy policy.

A New Approximation Method for the Shapley Value Applied to the WTC 9/11 Terrorist Attack

The Shapley value (Shapley (1953)) is one of the most prominent one-point solution concepts in cooperative game theory that divides revenues (or cost, power) that can be obtained by cooperation of players in the game. The Shapley value is mathematically characterized by properties that have appealing real-world interpretations and hence its use in practical settings is easily justified.The down part is that its computational complexity increases exponentially with the number of players in the game. Therefore, in practical problems that consist of more that 25 players the calculation of the Shapley value is usually too time expensive. Among others the Shapley value is applied in the analysis of terrorist networks (cf. Lindelauf et al. (2013)) which generally extend beyond the size of 25 players. In this paper we therefore present a new method to approximate the Shapley value by refining the random sampling method introduced by Castro et al. (2009). We show that our method outperforms the random sampling method, reducing the average error in the Shapley value approximation by almost 30%. Moreover, our new method enables us to analyze the extended WTC 9/11 network of Krebs (2002) that consists of 69 members. This in contrast to the restricted WTC 9/11 network considered in Lindelauf et al. (2013), that only considered the operational cells consisting of the 19 hijackers that conducted theattack

A New Approximation Method for the Shapley Value Applied to the WTC 9/11 Terrorist Attack

The Shapley value (Shapley (1953)) is one of the most prominent one-point solution concepts in cooperative game theory that divides revenues (or cost, power) that can be obtained by cooperation of players in the game. The Shapley value is mathematically characterized by properties that have appealing real-world interpretations and hence its use in practical settings is easily justified.The down part is that its computational complexity increases exponentially with the number of players in the game. Therefore, in practical problems that consist of more that 25 players the calculation of the Shapley value is usually too time expensive. Among others the Shapley value is applied in the analysis of terrorist networks (cf. Lindelauf et al. (2013)) which generally extend beyond the size of 25 players. In this paper we therefore present a new method to approximate the Shapley value by refining the random sampling method introduced by Castro et al. (2009). We show that our method outperforms the random sampling method, reducing the average error in the Shapley value approximation by almost 30%. Moreover, our new method enables us to analyze the extended WTC 9/11 network of Krebs (2002) that consists of 69 members. This in contrast to the restricted WTC 9/11 network considered in Lindelauf et al. (2013), that only considered the operational cells consisting of the 19 hijackers that conducted theattack

A New Approximation Method for the Shapley Value Applied to the WTC 9/11 Terrorist Attack

The Shapley value (Shapley (1953)) is one of the most prominent one-point solution concepts in cooperative game theory that divides revenues (or cost, power) that can be obtained by cooperation of players in the game. The Shapley value is mathematically characterized by properties that have appealing real-world interpretations and hence its use in practical settings is easily justified. The down part is that its computational complexity increases exponentially with the number of players in the game. Therefore, in practical problems that consist of more that 25 players the calculation of the Shapley value is usually too time expensive. Among others the Shapley value is applied in the analysis of terrorist networks (cf. Lindelauf et al. (2013)) which generally extend beyond the size of 25 players. In this paper we therefore present a new method to approximate the Shapley value by refining the random sampling method introduced by Castro et al. (2009). We show that our method outperforms the random sampling method, reducing the average error in the Shapley value approximation by almost 30%. Moreover, our new method enables us to analyze the extended WTC 9/11 network of Krebs (2002) that consists of 69 members. This in contrast to the restricted WTC 9/11 network considered in Lindelauf et al. (2013), that only considered the operational cells consisting of the 19 hijackers that conducted the attack