Systems and methods for determining whether to associate new user information with an existing user are disclosed. One embodiment involves clustering users in a set of users into clusters based on similarities of personal or behavioral features of the users. The embodiment further involves receiving new user information relating to a user using a device that provides the new user information via a computer network. A best matching cluster of the clusters is identified based on similarity of personal or behavioral features of the new user information to personal or behavioral features of the best matching cluster. The embodiment compares the personal or behavioral features of the new user information with personal or behavioral features of an existing user in the best matching cluster to determine whether to associate the new user information with the existing user or to assign it as a new (previously non-existent and unknown) user.