1. A method performed by data processing apparatus, the method comprising: receiving, from a data collection computer system, a data collection query provided by the data collection computer system to a data providing computer system requesting data from the data providing computer system that satisfies the data collection query, and an identifier referencing the data providing computer system; searching one or more computer-readable storage media for a modified data collection query in response to which the data providing computer system is configured to provide data; identifying the modified data collection query in response to searching the one or more computer-readable storage media, wherein the data providing computer system is configured to provide data that satisfies the modified data collection query instead of the data collection query; and providing the modified data collection query to the data providing computer system requesting data from the data providing computer system that satisfies the modified data collection query.