1. A computer-implemented method for classifying a client device requesting content from a server, comprising: monitoring a plurality of different events associated with the client device requesting content from the server; storing an evidence vector comprising information identifying the events that have occurred; determining a classification time in dependence on the evidence vector; and processing, when the classification time has been reached, the evidence vector to determine a classification for the client device, wherein the classification is indicative of a type of agent controlling the client device and the classification time is a time at which the classification may be determined with a predetermined level of confidence.