Embodiments include method, systems and computer program products for identifying unusual activity in an IT system based on user configurable message anomaly scoring. Aspects include receiving a message stream for the IT system and selecting a plurality of messages from the message stream that correspond to an interval. Aspects also include determining a message anomaly score for each of the plurality of the messages, wherein the message anomaly score for each of the plurality of the messages is determined to be one of a default message anomaly score and a custom message anomaly score and calculating an interval anomaly score for the interval by adding the message anomaly score for each of the plurality of the messages. Aspects further include identifying a priority level of the interval by comparing the interval anomaly score to one or more thresholds.