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. 2013;3:1544.
doi: 10.1038/srep01544.

Violent Extremist Group Ecologies Under Stress

Free PMC article

Violent Extremist Group Ecologies Under Stress

Manuel Cebrian et al. Sci Rep. .
Free PMC article


Violent extremist groups are currently making intensive use of Internet fora for recruitment to terrorism. These fora are under constant scrutiny by security agencies, private vigilante groups, and hackers, who sometimes shut them down with cybernetic attacks. However, there is a lack of experimental and formal understanding of the recruitment dynamics of online extremist fora and the effect of strategies to control them. Here, we utilize data on ten extremist fora that we collected for four years to develop a data-driven mathematical model that is the first attempt to measure whether (and how) these external attacks induce extremist fora to self-regulate. The results suggest that an increase in the number of groups targeted for attack causes an exponential increase in the cost of enforcement and an exponential decrease in its effectiveness. Thus, a policy to occasionally attack large groups can be very efficient for limiting violent output from these fora.


Figure 1
Figure 1. (TOP) Number of members participating in the 9 extremist fora under study.
Note that initially the fora grow exponentially and then saturate growing at a exponential yet much slower rate. (BOTTOM) Fora time shifted to match the early stages of the development of every fora and gain visual intuition on their dynamics. In particular, we aligned the early stages of the all fora with Forum 8, with the exception of Forum 5, which was aligned with Forum 9 due to a similar volume of members.
Figure 2
Figure 2. Fit of the model to the Forum 8 by minimizing root mean square error (RMSE) for the model with control (solid black line) and the uncontrolled one (solid blue).
Note that even when we add an additional parameter to the uncontrolled model (the number of susceptible individuals, N) the model without control cannot fit the data well (dashed line).
Figure 3
Figure 3. Simulated number of members of 25 randomly chosen fora out of 50 during a period of 10 years: I = 17,000,000, Nf = 50 , pR = 0.0026, , θ = 14, 000, and τ = 1 day, and λ = 9.49.
Figure 4
Figure 4. Total output and number of forum disruptions versus the policymaker threshold θ (lower values indicate stricter policies) using the same set of parameters as in Figure 3.

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