Google Chrome, Mozilla Firefox, and other major browsers are in the process of deprecating trust in certificates that were issued off Symantec Certificate Authority infrastructure. This includes Symantec, GeoTrust, Thawte, and RapidSSL certificates.
DigiCert will replace all affected certificates at no cost. Additionally, you do not need to switch to a new account or platform. Continue to use your current Symantec Website Security, GeoTrust, Thawte, or RapidSSL account to replace and order your SSL/TLS certificates.
What sites does this affect?
If your site is using a certificate in the Symantec group of brands that was issued before June 1, 2016, the Chrome 66 update is likely displaying warning messages to your users. For further details on the Chrome timeline, read this DigiCert blog post.
If you have a certificate affected by this distrust, your users will see a warning that their “connection is not private”, and "NET::ERR_CERT_SYMANTEC_LEGACY" error, as shown in the screenshot below.