A method comprising: displaying a popup window on an image forming apparatus to which at least one user terminal is connectable, the popup window corresponding to an event generated in the image forming apparatus, the displayed popup window having popped up to cover at least a portion of a previously displayed screen of the image forming apparatus, characterised by: when no user terminal is connected to the image forming apparatus, displaying the popup window on the image forming apparatus comprises displaying the popup window with a previously set first timeout applied to the popup window, and the method comprises closing the popup window if no user input with respect to the popup window is received during the first timeout after the popup window is displayed, and when a user terminal is connected to the image forming apparatus, displaying the popup window on the image forming apparatus comprises displaying the popup window with a previously set second timeout, different from the first timeout, applied to the popup window, and the method comprises transmitting, by the image forming apparatus to the user terminal, a popup window request to display, on the user terminal, a popup window corresponding to the event with the second timeout applied to the popup window displayed on the user terminal, and the method comprises closing the popup window on the image forming apparatus if no user input with respect to the popup window is received during the second timeout after the popup window is displayed, wherein the second timeout is longer than the first timeout. displaying a popup window on an image forming apparatus to which at least one user terminal is connectable, the popup window corresponding to an event generated in the image forming apparatus, the displayed popup window having popped up to cover at least a portion of a previously displayed screen of the image forming apparatus, characterised by: when no user terminal is connected to the image forming apparatus, displaying the popup window on the image forming apparatus comprises displaying the popup window with a previously set first timeout applied to the popup window, and the method comprises closing the popup window if no user input with respect to the popup window is received during the first timeout after the popup window is displayed, and when a user terminal is connected to the image forming apparatus, displaying the popup window on the image forming apparatus comprises displaying the popup window with a previously set second timeout, different from the first timeout, applied to the popup window, and the method comprises transmitting, by the image forming apparatus to the user terminal, a popup window request to display, on the user terminal, a popup window corresponding to the event with the second timeout applied to the popup window displayed on the user terminal, and the method comprises closing the popup window on the image forming apparatus if no user input with respect to the popup window is received during the second timeout after the popup window is displayed, when no user terminal is connected to the image forming apparatus, displaying the popup window on the image forming apparatus comprises displaying the popup window with a previously set first timeout applied to the popup window, and the method comprises closing the popup window if no user input with respect to the popup window is received during the first timeout after the popup window is displayed, and when a user terminal is connected to the image forming apparatus, displaying the popup window on the image forming apparatus comprises displaying the popup window with a previously set second timeout, different from the first timeout, applied to the popup window, and the method comprises transmitting, by the image forming apparatus to the user terminal, a popup window request to display, on the user terminal, a popup window corresponding to the event with the second timeout applied to the popup window displayed on the user terminal, and the method comprises closing the popup window on the image forming apparatus if no user input with respect to the popup window is received during the second timeout after the popup window is displayed, wherein the second timeout is longer than the first timeout.