1. A computer-implemented method comprising: anonymously linking, by one or more servers, a plurality of identifiers, including linking at least two different identifiers that are associated with two different requesting devices used by a same user to access content; identifying, by one or more servers, a user list associated with a topic, wherein the user list includes a separate entry for each different user that has been determined to satisfy the topic and having an identifier that is associated with a requesting device and further including information about a type of requesting device; updating, by the one or more servers, the user list including linking a single user identifier entry for the same user to other identifiers that have been assigned to the same user but are not included in the list, wherein the linking is based on the anonymous linking; receiving a content request from a user and associated user device; analyzing the user list including: determining that the content request is associated with a given user identifier that is not included in the user list; and determining that the given user identifier associated with the request is linked to the single user identifier entry that is included in the user list based on the linking; and selecting, based on the determination that the given user identifier is linked to the single user identifier entry that is included in the user list, content for delivery to the user device associated with the request based at least in part on the topic associated with the user list even though the given user identifier is not included in the user list.