1. An apparatus configured to classifying user traffic flows carried by a network, each user traffic flow being associated with one of a plurality of users, the apparatus comprising: a classification unit for classifying each user traffic flow into one of a plurality of traffic classes; a pattern generation unit for generating a user pattern for each user, each user pattern comprising the traffic class of each user traffic flow associated with said user; a grouping unit for grouping the plurality of users into one or more user groups based on the user pattern associated with each user, and for identifying a user pattern within each user group that is representative of all user patterns within the user group; and an optimised classification unit for identifying a user associated with a subsequent user traffic flow, determining the user group to which the user belongs, retrieving the representative user pattern of said user group, and using the traffic classes included in the representative user pattern to classify the subsequent user traffic flow.