MouseEvent triggered twice

programming flash
1 
stage.addEventListener(MouseEvent.MOUSE_UP, onmouseUp);
var container:Sprite = new Sprite()
var box = new myBox()//symbol from library
addChild(container)
container.addChild(box)
container.addEventListener(MouseEvent.MOUSE_UP, onmouseUpBox);
function onmouseUp(e:Event)
{
 trace("mouseUp From Stage")
}
 
function onmouseUpBox(e:Event)
{
 trace("mouse up from box")
}

At the moment when I click on the continer sprite, both mouse events are bringing triggered, from the stage and the container sprite. How can I make it so I only get the object I’m clicking on and not the stage as well??