The new version of Chrome released in January no longer supports SSL certificates issued by Symantec or any companies owned by them (Thawte, Verisign, Equifax, GeoTrust and RapidSSL) if issued before 1st June 2016.
What does this mean?
If you have a security certificate and your site has been HTTPS for a couple of years you will be wanting to renew the certificate. Why? Well, if a user happens to be using the latest Chrome to view your site they will get a warning which looks something like this.