Abstract: A system for facilitating real-time transactions of data representing monetary value between clients in a computer network comprises at least one first client and a transaction server computer system, the first client being associated with a set of data representing a balance of monetary value. The transaction server computer system is configured for receiving requests for transactions of data representing an amount of monetary value from a plurality of second clients for real-time updates of the first client's set of data. The first client's set of data is stored in a data structure comprising first and second subsets of the data, each subset of data defining a sub-balance representing an amount of monetary value. The first and second subsets are simultaneously updated following respective requests. A server architecture comprising a further administrative authority server computer system and secure tunnels enhances security.