1. A method comprising: detecting a request for provision of a first document, the first document being available for provision during a period of time, the request including an identifier of a network that referred the request; updating a count of referrals to the first document, the updating of the count being based on the identifier of the network that referred the request; and generating a second document based on the first document, the second document being a substitute for the first document subsequent to expiration of the period of time, the generating of the second document being responsive to the updated count of referrals transgressing a threshold value for the count of referrals, the generating of the second document being performed by a processor of a machine.