I remember the popup (e.g. new browser window) crisis circa 2000. Those were easy to stop because the behavior is easy for a browser to identify so browsers can't open popups if the action wasn't initiated by a user event handler and can open only so many in that condition.

Banners, modal dialogs and other kinds of "new popups" in general are a bit tougher. Usually there is some element you could remove from the DOM tree or display: none but the trouble is knowing which element!