Timely and appropriate reactions to detected denial-of-service attacks against computer networks are crucial in both civilian and military settings. GrADAR is an intuitive graph-based approach for assessing the effects of DoS attacks against computer networks so that response measures can be automatically selected without human intervention. However, GrADAR has limitations insofar as implicit effects of countermeasures are only taken into account by propagation towards user nodes. Possible effects in the other direction are only considered if they are explicitly specified. For this, they need to be exactly known in advance which is often infeasible. This contribution presents an extension to GrADAR, in which we consider resource workload and processing capabilities and their effects on resource availability. We incorporate workload measurements into the GrADAR model which are done by passive analysis of network traffic. We further augment the active availability probes with passive measurements. This ensures more accurate availability values because additional measurement traffic that might falsify results only needs to be injected when resources are currently not accessed.