Where to implement a JavaScript pop-up code

[cayne]

Hi everybody,
I got the following code, which I need to have on "forumhome" as well as "showthread", I simply added the code to the according templates on vBulletin 3.8.x - but now I've upgraded to v4 and when I just add the code it seems to generate longer loading times/general errors. So I'd like to ask, where's the right place to add such code. Thanks in advance.

Here's the code in question:

<script type="text/javascript" id="adcreative_script">
(function(){
var adcr = document.createElement('script');
adcr.type = 'text/javascript';
adcr.async = true;
adcr.src = '//static.adclickx.com/adcreative.js';
(document.getElementsByTagName('head')[0]||document.getElementsByTagName('body')[0]).appendChild(adcr);
})();
</script>