**4. Three types of terrorist attack scenarios**

to probability analysis, it is also necessary to apply the tools of game theory, which makes it

*Complex nature of the terrorist threat*: The presence of a terrorist organization in a region may give rise to the possibility of a broad spectrum of attack scenarios. Thus, to counter terrorist threats and terrorist mechanisms for initiating emergency situations to an even greater degree than for natural and man-made risks, a systemic approach is needed for ensuring security and developing an optimal strategy for counterterrorism force and resource deployment. Inasmuch as concentrating resources on protecting one system element (or protecting a target from one scenario of terrorist action) could prove useless because, after evaluating the situation, the terrorists could redirect the attack against another element of the system or switch to a different attack scenario. In this case, counterterrorism efforts will fail to reduce risk and increase the system's level of protection. *Presence of two-way linkages between the terrorist threat and system vulnerability*: The structure of linkages among the risk factors for the given *CES* in case of natural or manmade catastrophes is presented in **Figure** 3**a**. One differentiating feature of a terrorist risk assessment is the presence of two-way linkages (feedbacks) between the terrorist threat and (a) vulnerability of the system to the threat and (b) the magnitude of expected losses if the threat is successfully realized (see **Figure** 3**b**). This characteristic of terrorism must be examined in detail. In particular, reducing the vulnerability of a given system makes it possible to reduce substantially the level

In terrorist risk assessment framework, the main challenge is to estimate the probability of a terrorist attack. Some specialists believe that probabilistic measure is not adequate for the terrorist risk assessment since terrorist attack is not a stochastic event but a deliberate action based on the assessment made by terrorists regarding their skills and capabilities and the

Assignment of probabilities to the terrorist attack is a task which has a substantial human and behavioral dimension. The main problem is to describe the intentions of terrorists, their preferences, system of values (i.e., utility function), and decision rule. This allows assessing

**Figure 3.** (a) System of linkages among risk factors for natural or man-made hazards (safety context). (b) System of

possible to take into account the intentional actions of terrorists.

of the terrorist threat it faces.

262 Probabilistic Modeling in System Engineering

system's vulnerabilities.

probability of different attack scenarios.

linkages among risk factors for terrorist threat (security context).

Scenarios of terrorist attacks can be divided into three types, scenarios of ordinary, technological, and intelligent terrorism, that differ in resources used by terrorists to carry out the attacks and structure of losses inflicted by the attacks (**Figure** 1) [17–19].

Scenarios of ordinary terrorism imply organization of explosions, fires, and assassinations of officials, public figures, and people at large in order to intimidate people and destabilize political situation in the country or region. Scenarios of ordinary terrorism are not considered in this paper since these scenarios are not focused on complex engineering systems. We are going to deal with two other types of terrorist attack scenarios that are directly related to *CES.*
