Discourse is an open-source messaging platform. In versions 3.0.1 and prior on the "stable" branch and versions 3.1.0.beta2 and prior on the "beta" and "tests-passed" branches, the count of personal messages displayed for a tag is a count of all personal messages regardless of whether the personal message is visible to a given user. As a result, any users can technically poll a sensitive tag to determine if a new personal message is created even if the user does not have access to the personal message. In the patched versions, the count of personal messages tagged with a given tag is hidden by default. To revert to the old behaviour of displaying the count of personal messages for a given tag, an admin may enable the "display_personal_messages_tag_counts" site setting.