of them – cliques – is effective, the next step is to try out a number of attack strategies to see if any of them is effective against our defences, and in particular against cliques.

Of the attack strategies we tried against a clique defence, the best performer is an attack based on centrality. We used the centrality algorithm of Brandes [@Brandes01] to select the highest-centrality nodes for destruction at each round. As before, our calibration baseline is random replenishment. For this, the red and black graphs show performance against vertex-order and centrality attacks respectively. Both are equally effective; within two or three rounds the size of the largest connected component has been halved.

The green and blue graphs show that the same holds for rings: the network collapses completely after about a dozen rounds. Centrality attacks are very slightly more effective but there is not much in it.

\[htbp\] ![Rings and Cliques defense under vertex order and centrality attacks[]{data-label="fig:BA02"}](vertex-order-centrality-attack-rings-cliques.eps "fig:")\

The most interesting results from these simulations come from the magenta and cyan graphs, which show how cliques behave. Cyan shows, as before, a vertex-order attack with severity $m$ = 10 being ineffective against a clique defence. Magenta shows 