<div id="flashbanner">
This banner of UCH images requires Adobe Flash, Version 8 or above, to view.  
</div>       
<script type="text/javascript">
var so = new SWFObject("banner/banner_all.swf", "banner", "536", "150", "5", "#ffffff");
so.useExpressInstall('expressinstall.swf');
so.write("flashbanner");
</script>
关键就在红色的部分，查看代码：
第一帧：
// Action script...

// [Action in Frame 1]
Stage.scaleMode = "noscale";
com.deconcept.expressinstall.ExpressInstall.getInstance().loadUpdater();
// Action script...

// [Initial MovieClip Action of sprite 10]
#initclip 1
class com.deconcept.expressinstall.ExpressInstall
{
    var updater, hold, onEnterFrame;
    static var instance;
    function ExpressInstall()
    {
    } // End of the function
    static function getInstance()
    {
        if (com.deconcept.expressinstall.ExpressInstall.instance == undefined)
        {
            instance = new com.deconcept.expressinstall.ExpressInstall();
        } // end if
        return (com.deconcept.expressinstall.ExpressInstall.instance);
    } // End of the function
    function loadUpdater()
    {
        System.security.allowDomain("fpdownload.macromedia.com");
        var _self = this;
        updater = _root.createEmptyMovieClip("deconcept_expressInstallHolder", 10000007);
        updater.installStatus = _self.onInstallStatus;
        hold = updater.createEmptyMovieClip("hold", 1);
        updater.onEnterFrame = function ()
        {
            if (typeof(hold.startUpdate) == "function")
            {
                _self.initUpdater();
                onEnterFrame = null;
            } // end if
        };
        var _loc3 = Math.random();
        hold.loadMovie("http://fpdownload.macromedia.com/pub/flashplayer/update/current/swf/autoUpdater.swf?" + _loc3);
    } // End of the function
    function initUpdater()
    {
        hold.redirectURL = _root.MMredirectURL;
        hold.MMplayerType = _root.MMplayerType;
        hold.MMdoctitle = _root.MMdoctitle;
        hold.startUpdate();
    } // End of the function
    function onInstallStatus(msg)
    {
        if (msg == "Download.Complete")
        {
        }
        else if (msg == "Download.Cancelled")
        {
            getURL("javascript:alert(\'This content requires a more recent version of the Adobe Flash Player.\')");
        }
        else if (msg == "Download.Failed")
        {
            getURL("javascript:alert(\'There was an error downloading the Flash Player update. Please try again later, or visit adobe.com/go/getflashplayer/ to download the latest version of the Flash plugin.\')");
        } // end else if
    } // End of the function
} // End of Class
#endinitclip
很显然，这个代码的意思是直接提示网页没有安装flash文件，从而弹出js提示！
有兴趣看：http://www.uch.ie/首页