A first individual enters an offer to sell a security on a first data processing system. This offer is sent to a server over a communication network which is available to the public. From the server, the offer is transmitted to additional data processing systems which are connected to the publicly-available communication network. The first user's offer is eventually sent to a second data processing system, where a second individual enters an acceptance to the first user's offer to sell a security. This second user's acceptance is then transmitted back to the server over the publicly-available communication network. Upon the arrival of the acceptance, an account belonging to the second user is debited for the amount of the security just purchased, and the second user obtains title to the securities.