Classification and verification of static file transfer protocols is provided. A network node sitting in the path of packets classifies traffic according to its content, and then statistically verifies that the content actually matches the initial classification. Classification and verification are standard building blocks in networks systems that provide quality-of-service. However, unlike traditional quality-of-service building blocks, a system of the present invention takes a trust-but-verify approach, and thus can rely on longer-timescale statistical online or offline verification to reduce computational requirements. This improves scalability and reduces the cost and complexity that in part has prevented prior service differentiation systems from succeeding in the Internet. Internet Service Providers (ISPs) can combine the classification and verification building blocks with a networked directory service to allow further classification as to whether particular content is for pay.