View larger image | When networks depend on other networks, such as a communications network that relies on a power grid, failure can cascade back and forth between the two. This behavior may explain sudden breakdowns in interacting systems. Thus, the effects of an attack on a single node can reduce an übernetwork (above) that starts with 12 operating nodes to just four. Credit: Source: S.V. Buldyrev et al/Nature 2010, adapted byT. Dubé