15. A non-transitory machine-readable storage medium comprising instructions that, when executed by one or more processors of a machine, cause the machine to perform operations comprising: detecting, by one or more processor of a machine, a request for provision of a first document that is available for provision; updating a count of referrals upon detecting a request sent from a set of one or more networks for provision of the first document; generating a second document based on the first document, the second document being a substitute for the first document subsequent to the first document becoming unavailable for provision, the generating of the second document being responsive to a determination that the updated count of referrals has transgressed a predetermined threshold value, the generating of the second document being performed by one or more processor of the machine; and providing the second document in lieu of the first document when the first document is requested subsequent to the first document becoming unavailable upon expiration of a predetermined time of availability of the first document.
15. A non-transitory machine-readable storage medium comprising instructions that, when executed by one or more processors of a machine, cause the machine to perform operations comprising: detecting, by one or more processor of a machine, a request for provision of a first document that is available for provision; updating a count of referrals upon detecting a request sent from a set of one or more networks for provision of the first document; generating a second document based on the first document, the second document being a substitute for the first document subsequent to the first document becoming unavailable for provision, the generating of the second document being responsive to a determination that the updated count of referrals has transgressed a predetermined threshold value, the generating of the second document being performed by one or more processor of the machine; and providing the second document in lieu of the first document when the first document is requested subsequent to the first document becoming unavailable upon expiration of a predetermined time of availability of the first document. 16. The non-transitory machine-readable storage medium of claim 15 , wherein the first document includes an identifier of a network that referred the request.