Symantec has fired an undisclosed number of employees after they were caught issuing unauthorized cryptographic certificates that made it possible to impersonate HTTPS-protected Google webpages.

"We learned on Wednesday that a small number of test certificates were inappropriately issued internally this week for three domains during product testing," Symantec officials wrote in a blog post published Friday. "All of these test certificates and keys were always within our control and were immediately revoked when we discovered the issue. There was no direct impact to any of the domains and never any danger to the Internet."

The post went on to say that the unnamed employees were terminated for failing to follow Symantec policies. Symantec officials didn't identify the three domains the test certificates covered, but in a separate blog post, Google researchers said Symantec’s Thawte-branded certificate authority service issued an Extended Validation pre-certificate for the domains google.com and www.google.com.

"This pre-certificate was neither requested nor authorized by Google," they wrote.

The unauthorized certificate came to light after Google employees monitored logs associated with Google's Certificate Transparency project. The program is designed to fix several structural flaws in the way HTTPS certificates are issued by providing an easy way to monitor their generation in real time. Among other things, the project makes it possible to detect transport layer security credentials that have been mistakenly issued by a browser-trusted certificate authority. The ability for Google employees to independently discover the unauthorized certificates so quickly is a strong endorsement of the effectiveness of the Certificate Transparency program.

The incident came five months after Google warned of a separate batch of bogus certificates that had been issued for several of its domains , including *.google.com, *.google.com.eg, *.g.doubleclick.net, *.gstatic.com, www.google.com, www.gmail.com, and *.googleapis.com. They were issued by Egypt-based MCS Holdings, an intermediate certificate authority that operates under the China Internet Network Information Center (CNNIC). The Chinese domain registrar and certificate authority, in turn, is included in root stores for virtually all OSes and browsers.

Since last week's discovery of the certificate issued by Thawte, Google has updated its Chrome browser to block it. In any event, Google researchers said they don't believe the pre-certificate was used in any attacks or represented a threat to Google visitors because it was valid only for one day.