title: IE gives Certificate warning although my website is served over http
body: <p>I'm currently working on a website for a client, that is served over HTTP as it mostly contains static content. However, in some Windows Configurations Internet Explorer gives a warning, that my security certificate isn't valid. </p>
  
  <p>The site is made with a custom WordPress theme. Could it be that some plugin is the culprit of this problem? All my javascript libraries and stylesheets are also loaded over HTTP. Or are there any other common mistakes that I could have made?</p>
  
  <p>The website URL is <a href="http://wolfgang-augsten.at" rel="nofollow">http://wolfgang-augsten.at</a>. </p>