The present disclosure relates to a computer-implemented method and an apparatus for classifying anomalies of one or more feature-associated anomalies in network data traffic between devices in a first part of a network and devices in a second part of the network. The method comprises retrieving at least one network data traffic sample and determining one or more feature-associated anomaly scores for the retrieved at least one network data traffic sample. The method further comprises determining feature importance of each feature of a feature-associated anomaly score and classifying one or more anomalies based on the determined one or more feature-associated anomaly scores and the determined feature importance.