Apparatus, systems, and methods may operate to generate a reference statistical model of an operating system, such as a computer system, and display the reference statistical model as a hierarchical, segmented time series event stream graph, along with a graph representing current behavior of the system. The event stream graph may be derived from one or more streams of security events. Additional operations may include receiving requests to display further detail respecting discrepancies between the reference statistical model and the current behavior. Other apparatus, systems, and methods are disclosed.