The masking problem comes in continue to the ghosting. When masking is occurred, the controller cannot detect a key change that has occur. Suppose for example that the ghosting problem has occur, by pressing C2, B2 and B3 simultaneously, like the previous example. The controller will think that the button C2 C3 is pressed, although the operator has not pressed C3. Now, the operator presses the button C3 without releasing any other button. Nothing changes at the microcontroller. And now the operator releases the button C2... What happens? Nothing! The microcontroller still thinks that C2 is pressed and cannot detect the button release! This is the masking problem, also a gamers headache.