Improved systems, methods, and programs for customized distribution of data, particularly financial data. Individual users of networked computer systems have the capability to select and receive data from data streams produced by sources and made available simultaneously and in standardized format to numbers of client terminals. Selected data is mapped according to individual user specifications and may be used in client applications such as databases or spreadsheets, and stored in caches until users are ready to receive it. Data may be formatted and sent back to the stream source for use in applications operated at the source. The system also facilitates checking of data integrity, in particular by comparing sequences of records sent by the source and received by the client system.