Mobile banking system and method

The invention provides a method and system for operating a banking service. The system has a database for storing customer data including a mobile telephone number and a corresponding customer password for each customer. A message server is arranged to receive transaction request messages sent from mobile telephones of customers, the transaction request messages including predetermined content comprising alphanumeric characters entered by the customers. The message server transmits a password request message to the customer's mobile telephone, requesting the customer to enter a password. A transaction server is arranged to identify customers from the numbers of the customers' mobile telephones included in data transmitted via the message server, and to receive passwords entered by customers and transmitted via the message server. If a password corresponds to a respective mobile telephone number in the recorded customer data, the transaction server authorizes a transaction corresponding to the predetermined content of the transaction request message sent from the mobile telephone of the customer. The transaction request message may be wholly predetermined and comprise an alphanumeric component identifying the nature or type of the transaction and a numeric value indicating the monetary value of the transaction, or may include both a predetermined and a variable component.