A computer program product comprising a non-transitory machine-readable medium that stores a program, the program being executed by a machine to perform a method of identifying a network-connected entity across multiple device-, usage- and application- domains, the method comprising: maintaining a database comprising entity identities, wherein an entity identity has associated therewith a set of encoded feature data; periodically updating the database by merging into a unique entity identity one or more entity identities that are found to represent a same entity by the following sub-steps: computing weights for each set of encoded feature data, the weights indicating an estimated ability to correctly identify a match or a non-match between entity identities; and calculating, using the weights, the probability that two or more sets of encoded feature data match and represent the same entity identity; wherein probabilities above a first threshold are considered to be matches indicating that two or more entity identities are to be merged into a unique entity identity, and wherein probabilities below a second threshold are considered to be non-matches; responsive to a request for content, the request having associated therewith usage feature data associated with the network-connected entity to be identified: applying a probabilistic matching function to a measure of closeness between the usage feature data associated with the request and the sets of encoded feature data associated respectively with the entity identities in the database; as a result of applying the probabilistic matching function, determining if the request is recognized as originating from an entity whose entity identity is stored in the database; and if the request is recognized as originating from an entity whose entity identity is stored in the database, using the entity identity to construct a response to the request for content. maintaining a database comprising entity identities, wherein an entity identity has associated therewith a set of encoded feature data; periodically updating the database by merging into a unique entity identity one or more entity identities that are found to represent a same entity by the following sub-steps: computing weights for each set of encoded feature data, the weights indicating an estimated ability to correctly identify a match or a non-match between entity identities; and calculating, using the weights, the probability that two or more sets of encoded feature data match and represent the same entity identity; wherein probabilities above a first threshold are considered to be matches indicating that two or more entity identities are to be merged into a unique entity identity, and wherein probabilities below a second threshold are considered to be non-matches; computing weights for each set of encoded feature data, the weights indicating an estimated ability to correctly identify a match or a non-match between entity identities; and calculating, using the weights, the probability that two or more sets of encoded feature data match and represent the same entity identity; wherein probabilities above a first threshold are considered to be matches indicating that two or more entity identities are to be merged into a unique entity identity, and wherein probabilities below a second threshold are considered to be non-matches; responsive to a request for content, the request having associated therewith usage feature data associated with the network-connected entity to be identified: applying a probabilistic matching function to a measure of closeness between the usage feature data associated with the request and the sets of encoded feature data associated respectively with the entity identities in the database; as a result of applying the probabilistic matching function, determining if the request is recognized as originating from an entity whose entity identity is stored in the database; and if the request is recognized as originating from an entity whose entity identity is stored in the database, using the entity identity to construct a response to the request for content.