Finding the root-cause of a network security anomaly is essential for network operators. In our recent work [1, 5], we introduced a generic technique that uses frequent itemset mining to automatically extract and summarize the traffic flows causing an anomaly. Our evaluation using two different anomaly detectors (including a commercial one) showed that our approach works surprisingly well extracting the anomalous flows in most studied cases using sampled and unsampled NetFlow traces from two networks. In this demonstration, we will showcase an open-source anomaly-extraction system based on our technique, which we integrated with a commercial anomaly detector and use in the NOC of the GÉANT network since late 2009. We will report a number of detected security anomalies and will illustrate how an operator can use our system to automatically extract and summarize anomalous flows.