You visit a client or other website and, instead of the site itself, you encounter a security certificate error. If you are using Windows and Internet Explorer, the ...

Most people using Internet Explorer have encountered a security certificate error such as "There is a problem with this website's security certificate" at some point ...

While browsing a website on Google Chrome, if you get an error saying This server could not prove that it is <domain.com>; its security certificate is not from <ABC ...

The name on the security certificate is invalid or does not match the name of the target site webmail.domain.com. Outlook is unable to connect to the proxy Server ...

I'm getting errors related to an expired security certificate from noembed.com when I load the mobile version of a front page article's comments in desktop IE.

Cybercriminals are distributing malware using fake security certificate update requests displayed on previously compromised websites, attempting to infect potential victims with backdoors and Trojans ...

So, if an antivirus program or a network is intercepting a connection with a security certificate issued by a CA that is not in the Mozilla CA store, the connection is considered unsafe.