10. A system for providing a seed Uniform Resource Locator (URL) of a document within a computer network to a search engine in the computer network, the computer network having a plurality of documents with URLs distributed therein, the search engine having a web-graph in which exists a set of crawled documents, the system comprising: a network interface for communicating with the computer network; and a hardware processor coupled to the network interface, the hardware processor configured to execute software stored in a non-transitory computer-readable medium to: detect, from among data packets exchanged in the computer network external to the search engine, a packet containing a request to access a requested document; extract a requested document URL of the requested document from the packet containing the request; and determine that the requested document URL was not previously requested within a predetermined time interval, and in response, provide the requested document URL as the seed URL to the search engine so as to cause the search engine to expand the set of crawled documents by adding the requested document to the set of crawled documents; and wherein the hardware processor is not aware of which documents are not reachable by the search engine.
10. A system for providing a seed Uniform Resource Locator (URL) of a document within a computer network to a search engine in the computer network, the computer network having a plurality of documents with URLs distributed therein, the search engine having a web-graph in which exists a set of crawled documents, the system comprising: a network interface for communicating with the computer network; and a hardware processor coupled to the network interface, the hardware processor configured to execute software stored in a non-transitory computer-readable medium to: detect, from among data packets exchanged in the computer network external to the search engine, a packet containing a request to access a requested document; extract a requested document URL of the requested document from the packet containing the request; and determine that the requested document URL was not previously requested within a predetermined time interval, and in response, provide the requested document URL as the seed URL to the search engine so as to cause the search engine to expand the set of crawled documents by adding the requested document to the set of crawled documents; and wherein the hardware processor is not aware of which documents are not reachable by the search engine. 12. The system according to claim 10 , wherein the documents comprise Web pages.