Abstract. Naor and Pinkas introduced metering schemes at Eurocrypt ’98 in order to decide on advertisement fees for web servers. In the schemes, any server should be able to construct a proof to be sent to an audit agency if and only if it has been visited by at least a certain number, say k, of clients. This paper first shows an attack for their schemes such that only two malicious clients can prevent a server from computing a correct proof. We next present provably secure metering schemes. Finally, an efficient robust secret sharing scheme is derived from our metering scheme.