A computer-implemented method for determining computer system security threats, the computer system including user accounts established on the computer system, the method including the steps of: (i) for a plurality of user accounts, assigning a risk level to each account; (ii) in a time interval, for a plurality of events, wherein each event is linked to a respective user account, assigning an event score relating to deviation from normal behavior of each event with respect to the respective user account; (iii) in the time interval, for the plurality of events, calculating an event importance which is a function of the respective event score and the respective user account risk level; (iv) prioritizing the plurality of events by event importance, and (v) providing a record of the plurality of events, prioritized by event importance.