A client-server type computer system for graphical applications is provided, that is to say, for displaying data in the form of software units called “widgets” on display screens called “display units”, said system being intended to control the operation of a machine, the machine including at least one human-machine interface allowing interaction with the widgets, said system managing critical data or functions. The computer system includes a securing engine controlling the integrity of the display of the critical widgets, the sending of commands which is performed by means of the human-machine interface, the input and display of the critical data. The main provisions of this securing engine are the use of computer “signatures”, the provision of “feedback” circuits and the use of guard mechanisms or dedicated confirmation dialog boxes. Preferably, the machine is an aircraft, the computer system is the avionics on board said aircraft and the display screens are the cockpit display systems.