1. A user correlation system, comprising: one or more processors configured to: receive a unique identifier association request for unique identifiers; identify a first website containing user activity information associated with a first one of the unique identifiers; extract a first set of data from the user activity information on the first website associated with the first one of the unique identifiers; identify a second website containing user activity information associated with a second one of the unique identifiers; extract a second set of data from the user activity information on the second website associated with the second one of the unique identifiers; search for similarities between the first set of data extracted from the user activity information on the first website and the second set of data extracted from the user activity information on the second website; compare the first set of data extracted from the first website with the second set of data extracted from the second website; and generate an association score that indicates a confidence factor that the first one of the unique identifiers and the second one of the unique identifiers are associated with a same user according to the comparison between the first set of data and the second set of data.