To provide secure single-source panel audience measurement data while providing confidentiality and security of panel membership, an audience measurement server may capture content identifiers and client identifiers of devices receiving content. A panel provider may generate a probabilistic data structure via a hash of the client identifiers. The audience measurement server may utilize the filter array to extract a subset of measurement data including the data of the panel members, as well as data of some non-panel members as false positives, without being able to distinguish between the members and non-members. The audience measurement server may encrypt the extracted subset of data with each client identifier corresponding to an item of data as a key, and send the encrypted data to the panel provider, thus including both panel and some non-panel data, with the panel provider only able to decrypt data corresponding to its own panel members.