In one embodiment, a method includes receiving identifier-information from a device of a first user, wherein the identifier-information is associated with a source of an incoming communication; accessing a social graph including nodes and edges, where the nodes include a first node corresponding to the first user, and second nodes corresponding to second users; determining whether one or more reporting users, corresponding to second nodes within a specified degree of separation from the first node, have flagged the source of the incoming communication as a spam source; and sending, to the first user, a spam-notification object that includes information identifying one or more of the reporting users.