Malware links in my coupon site?

Hey,

Yesterday I noticed that every page of my WordPress site has this code in it before the </head> tag:

<div id="fb4727564">
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<a href="https://www.usa-casino.me">
<img src="https://www.usa-casino.me/wp-content/uploads/2013/09/Online-Casino-USA-275x300.jpg" alt="additional online casino usa hints" /></a>
 review sports. <script type="text/javascript">document.getElementById("fb4727564").innerHTML = '';
</script>
</div>

I need this removed and the source of where it’s coming from.
Does anyone know what I can do about this? I’ve tried several WordPress security plugins but none of them have been able to detect the problem.

Thanks!