Connections between individuals facilitate the exchange of goods, resources and information and create benefits. These connections may be exploited by adversaries to spread their attacks as well. What is the optimal way to design and defend networks in the face of attacks We develop a model with a Designer and an Adversary. The Designer moves first and chooses a network and an allocation of defense resources across nodes. The Adversary then allocates attack resources on nodes and determines how successful attacks should navigate the network. Our main result is that, in a wide variety of circumstances, a star network with all defense resources allocated to the central hub node is optimal for the Designer. The Adversary targets undefended peripheral nodes; upon capture of these nodes the resources mount a concerted attack on the center.
