This is how!

<script type="text/javascript">
    var adblock = true;
</script>
<script type="text/javascript" src="adframe.js"></script>
<script type="text/javascript">
    if(adblock) {
          //adblock is installed and enabled on this site :-D
    }
</script>

adframe.js:

adblock = false;

Source: http://stackoverflow.com/questions/18180598/ad-blocker-detection-aka-adblock-plus