Abstract: A traffic authentication method and related computer-implemented software provide authenticated information about audio or video program traffic transmitted over a computer network from a media server. The invention combines server-side measurement with client-side sampled verification. The server-side measurement provides a complete and accurate measurement of audience size for media traffic transmitted from the server. The client-side sampled verification provides sampled corroboration of the veracity or accuracy of part of the transmitted media traffic. One method implementation includes forming at the media server a media census of media segments (e.g., advertisements) transmitted over a computer network from the media server, forming at one or more client computers media segment receipts that identify media segments transmitted to the one or more client computers from the media server; and correlating the media census with the media segment receipts to provide verification of the media census.