We describe a framework for managing network attack graph complexity through interactive visualization, which includes hierarchical aggregation of graph elements. Aggregation collapses non-overlapping subgraphs of the attack graph to single graph vertices, providing compression of attack graph complexity. Our aggregation is recursive (nested), according to a predefined aggregation hierarchy. This hierarchy establishes rules at each level of aggregation, with the rules being based on either common attribute values of attack graph elements or attack graph connectedness. The higher levels of the aggregation hierarchy nd to higher levels of abstraction, providing progressively summarized visual overviews of the attack graph. We describe rich visual representations that capture relationships among our ally-relevant attack graph abstractions, and our views support mixtures of elements at all levels of the aggregation hierarchy. While it would be possible to allow arbitrary nested aggregatio...