found that rings were all but useless, while cliques are remarkably effective. This may be part of the reason why cell structures have been widely used by capable insurgent groups.

Next, we searched for attacks that work better against clique defences. We found that the centrality attack of Holme et al does indeed appear to be more powerful, although it can be more difficult to mount as evaluating node centrality involves knowledge of the entire topology of the network. Centrality attacks may reflect the modern reality of counterinsurgency based on pervasive communications intelligence and, in particular, traffic analysis.

Now we are searching for defences that work better against centrality attacks. A promising candidate appears to be the delegation defence, combined with cliques. This combination may in some ways reflect the reported ‘virtualisation’ strategies of some modern insurgent networks.

Above all, this work provides a systematic way to evolve and test security concepts relating to the topology of networks. Clearly the coevolution of attack and defense can be taken much further. Further work includes testing:

1.  networks that grow or shrink, maybe with endogenous replenishment (current recruitment a function of past operational success)

2.  imperfectly informed attackers, such as policemen who 