At SMX last week, Gary lllyes from Google said on the How to secure your site for Google's HTTPS algorithm that about 0.5%of security certificates are broken certificates. He is experimenting with trying to address the problem in Google search results. Gary said that he is working on an internal experiment to flag sites having broken security certificates. Gary allies also said that they are going to boost rankings for secure login pages even more than that they do with a normal HTTPS ranking boost. Google takes web security seriously and will adapt the HTTPS algorithm.
