Methods, systems, and apparatus, including computer programs encoded on computer storage media, for determining a network path between computer assets. One of the methods includes receiving an asset topology that includes an identifier for each computer-related asset that may be an entry point for an attack simulation, receiving threat data that identifies vulnerabilities of computer-related assets, determining a first computer-related asset that may be an entry point for an attack simulation, identifying one or more first vulnerabilities of the first computer-related asset, determining a path from the first computer-related asset to a second computer-related asset, determining one or more second vulnerabilities of the second computer-related asset, determining a probability that the second computer-related asset will be compromised by an adversary, and determining a change to the asset topology to reduce the probability that the second computer-related asset will be compromised by an adversary.