A display device is disclosed which may be used in a mobile telephone or other article which is intended to make secure transactions such as financial transactions, as well as other personal transactions such as telephone calls. The device includes a display (24) for displaying information, a financial transaction controller (26) including a processor (28), a display driver (30) for driving the display (24) and a secure memory (32). The financial transaction controller allows the display section (24), and an input keypad (12), to operate under the control of the device to enable personal functions other than financial transactions to be performed. However, in the event of a financial transaction, the financial transaction controller takes over control of the display section (24) and the input keypad (12) so that the financial transaction can be performed while the device is under the control of the financial transaction controller to thereby prevent tampering with or tapping off of data, and also the display of information other than under the control of the financial controller.