Earlier this week, Google revealed in a blogpost that it will no longer be accepting Symantec security certificates issued before June 2016 as valid and trusted once Chrome 66 is released in 2018.
Symantec will be switching certificate issuance to DigiCert infrastructure by December 1. Google says anything based on the prior infrastructure after the same date will not be trusted by Chrome as well.
The plan was initially floated last July, with Google saying that it gave Symantec ample time to revamp its infrastructure to comply with industry standards. The recent announcement serves as an official notice to webmasters so they can prepare for the changes.
Chrome version 66 is scheduled to be released to beta users on March 15, 2018, and to standard users on April 17, 2018.