This morning and yesterday, the webmaster forums started getting polluted with questions about Google Webmaster Tools issues and notifying them about SSL certificate errors.
In short, back in 2009, Google began notifying webmasters of security certificate issues. All of a sudden, yesterday, tons of people started getting them all at once.
Some of the messages, webmasters are claiming are sent in error. Either the certificate works fine or the site does not have SSL at all on it. One webmaster wrote, "I got the same message, and it's irritating, because we don't us SSL."
Google has not responded to any of the threads at the time of publishing this story.
Update: John Mueller told me:
These are legitimate messages (the SSL certificate is really incorrect). That can happen if your hoster lets your server respond on HTTPS, but doesn't actually set up a correct certificate there. This is a problem because it either shows errors in the browser, or gives users a false sense of security when they use those URLs.
That said, it looks like we might be sending out a bit too many of these messages at the moment, for example for servers that serve HTTPS content but don't actually use it at all. We'll look into the specifics and see if we can pause the messages for the moment. Show less