Strange code from domain mapping plugin in head

Hi there,
My client asks what this code in the header means:
<script type="text/javascript" src="http://www.webzenz.nl/dm-sso-endpoint/1432827029/?dm_action=domainmap-setup-cdsso"></script>
When clicked on, it leads to a 404...
I never noticed it before, hope that someone can explain.
Example: view-source:www.acaciagroenkunst.nl

Thanks in advance for helping, cheers!