Most probably this error is shown in chrome browser when you visit a secured website URL starting with HTTPS. It because the page may be loading any one or more scripts from an unsecured source. For example a plugin script with a HTTP link or an ad code with a HTTP link can be the culprit. So the website owner should change all those unsecured links to secured links. All links starting with http should be changed to https in the source pages to avoid these kind of errors that making the visitors panic.