1. A computer system for risk assessment, comprising: one or more processor; and one or more storage devices having stored thereon computer-executable instructions, which are executable by the one or more processors to cause the computer system to: evaluate historical authentication data to identify a set of authentication context properties associated with user authentication sessions; evaluate compromised user account data to identify a set of malicious account context properties associated with at least one of compromised user accounts or compromised user authentication events; annotate the set of authentication context properties and the set of malicious account context properties to create an annotated context properties training set; train a plurality of risk assessment machine learning modules based upon the annotated context properties training set to generate a plurality of risk assessment models, wherein each risk assessment model is responsive to a predefined context property; identify a current user account event of a current user; evaluate a first current user context property of the current user using a first risk assessment model; evaluate a second current user context property of the current user using a second risk assessment model; aggregate results from the first and the second risk assessment models to generate a risk analysis metric; moderate the current user account event based upon the risk analysis metric; apply the aggregated results from the first and the second risk assessment models to prior user account events of a user to generate an evaluation metric; and retroactively ban or unban the current user account based upon the evaluation metric.