Have a Coding Question For Any Tech Geeks Please... Have I Been Hacked?

I have a WordPress site. Just today, when I approve comments for visitor's posts, this code gets inserted automatically after the commenter's email address (which I remove, obviously, before approving):

* <![CDATA[ */(function(){try{var s,a,i,j,r,c,l,b=document.getElementsByTagName("script");l=b[b​.length-1].previousSibling;a=l.getAttribute('data-cfemail');i​f(a){s='';r=parseInt(a.substr(0,2),16);for(j=2;a.length-j;j+=​2){c=parseInt(a.substr(j,2),16)^r;s+=String.fromCharCode(c);}​s=document.createTextNode(s);l.parentNode.replaceChild(s,l);}​}catch(e){}})();/* ]]> */

Can anyone tell me what this is?

And, most importantly, how to stop this?