Google and Mozilla engineers found that Symantec misissuing 30,000 SSL certificates in March 2017. Google will begin to distrust all existing certificates in Chrome starting with October 2018. Google and other browser vendors hope that by offloading the SSL. issuance process to another CA’s infrastructure, it will prevent SymantEC from breaking the rules and issuing certificates for sites it shouldn’t. Google proposed this measure this spring, Symantech has acknowledged it in June and approved to it on mid-July.
Source: https://www.bleepingcomputer.com/news/security/google-outlines-ssl-apocalypse-for-symantec-certificates/