A processing system may obtain a first sampled flow record for a first flow in a network, comprising information regarding selected packets of the first flow, derive, from the first sampled flow record, a data volume and a duration of the first flow, and determine a first flow metric for the first flow that is calculated from the data volume and the duration, where the first flow metric is one of a plurality of flow metrics for a plurality of flows, and where the plurality of flow metrics is determined from the plurality of sampled flow records associated with the plurality of flows. The processing system may then classify the first flow into one of at least two classes, based upon the first flow metric and at least a first flow metric threshold.