A method for secure online audience measurement, comprising: receiving, by an audience measurement server executed by a first device, a communication transmitted from each of a plurality of client devices, each communication comprising an identification of an item of content and a device identifier of said client device, a first portion of the plurality of client devices operating on behalf of members of a panel measurement service; receiving, by the audience measurement server from a second device, a request for measurement data of the members of the panel measurement service, the request comprising a probabilistic data structure corresponding to a hash of each device identifier of the first portion of the plurality of client devices; filtering, by the audience measurement server via the probabilistic data structure, the received communications to select a subset of the received communications, the subset including (i) the communications including device identifiers of the first portion of the plurality of client devices and (ii) the communications including device identifiers of a second portion of the plurality of client devices not corresponding to panel members; encrypting, by the audience measurement server, for each communication in the selected subset, the identification of the item of content using the corresponding device identifier in each said communication to generate encrypted measurement data; and transmitting, by the audience measurement server to the second device, the encrypted measurement data; wherein the second device successfully decrypts identifications of items of content corresponding to device identifiers of the first portion of the plurality of client devices, and fails to decrypt identifications of items of content not corresponding to device identifiers of the first portion of the plurality of client devices. receiving, by an audience measurement server executed by a first device, a communication transmitted from each of a plurality of client devices, each communication comprising an identification of an item of content and a device identifier of said client device, a first portion of the plurality of client devices operating on behalf of members of a panel measurement service; receiving, by the audience measurement server from a second device, a request for measurement data of the members of the panel measurement service, the request comprising a probabilistic data structure corresponding to a hash of each device identifier of the first portion of the plurality of client devices; filtering, by the audience measurement server via the probabilistic data structure, the received communications to select a subset of the received communications, the subset including (i) the communications including device identifiers of the first portion of the plurality of client devices and (ii) the communications including device identifiers of a second portion of the plurality of client devices not corresponding to panel members; encrypting, by the audience measurement server, for each communication in the selected subset, the identification of the item of content using the corresponding device identifier in each said communication to generate encrypted measurement data; and transmitting, by the audience measurement server to the second device, the encrypted measurement data;