One of the new security features in Interent Explorer makes you click on a Flash object to "activate" it. It sounds like this will make sure that the only entity that uses the object is the user since you have to click on it.
Until you activate the object it has a border around the object. I used to ignore it as a minor display issue, but I had to fix a site that had a Flash object behind a drop-down menu and was causing people to click the menu twice to go anywhere. (First click activated the Flash object and the second click worked like normal.)
The document write solution is listed on this Adobe Developer Article.