2. The method of claim 1 further comprising: maintaining the social graph comprising: using activity information stored at the storage server, determining a plurality of nodes representing persons specified in a plurality of activity information stored at the storage server; generating a plurality of edges in the social graph, wherein each edge represents at least one activity information of the plurality of activity information; and using the plurality of edges to couple the plurality of nodes.
1. A method comprising: receiving first activity information for a sender of a first link to at least one recipient collected by a collection resource at a Web site, wherein 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 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 recipient collected in collecting the second activity information; using at least one processor, attempting to identify a first node representative of the sender in a social graph; when a first node representative of the sender in a social graph is not identified and after receiving the second activity information, creating a second node to represent the sender in the social graph; and using the social graph, selecting a personalized digital content for delivery to the recipient.