1. A method comprising: receiving first activity information for a sender of a message sent to at least one recipient by a collection resource at a Web site, wherein the message comprises text associated with the Web site, the collection resource adds a first link to the message, and no personally identifiable information of the sender is collected in collecting the first activity information; storing the first activity information at a storage server; receiving second activity information when a first recipient accesses the first link sent by the sender corresponding to the first activity information stored at the storage server, wherein no personally identifiable information of the first recipient is collected in the second activity information; using at least one processor, using the first activity information to identify a first node in a social graph as being representative of the sender, wherein the using the first activity information to identify a first node in a social graph as being representative of the sender comprises: extracting a user identifier from a cookie received with the first activity information; and if a match for the user identifier is not found in the social graph, performing a fingerprinting approach using attributes comprising at least one of device identifiers; Internet Protocol (IP) addresses; operating systems; browsers types; browser versions; or user navigational, geo-temporal, or behavioral patterns; or any combination of these; using the second activity information to identify a second node in the social graph as being representative of the first recipient; determining a category for the first link as a first category type; identifying a first edge between the first and second nodes is representative of the first category type; in the social graph, updating a value of the first edge between the first and second nodes; and after a first amount of time has passed, altering the value of the first edge.