Google announced about adjusting the indexing system looking for more HTTPS pages. More specifically they will be looking for HTTPS equivalents of HTTP pages even if the HTTPS pages are not linked to any page.
Google said: “When two URLs from the same domain appear to have the same content but are served over different protocol schemes, we’ll typically choose to index the HTTPS URL if:
- It doesn’t contain insecure dependencies.
- It isn’t blocked from crawling by robots.txt.
- It doesn’t redirect users to or through an insecure HTTP page.
- It doesn’t have a rel="canonical" link to the HTTP page.
- It doesn’t contain a noindex robots meta tag.
- It doesn’t have on-host outlinks to HTTP URLs.
- The sitemaps lists the HTTPS URL, or doesn’t list the HTTP version of the URL
- The server has a valid TLS certificate.”
Google picks the HTTPS version by default, other search engines can be also be directed to do the same by redirecting the HTTP site to the HTTPS site and implementing the HSTS header on the server.Google to Index HTTPS Pages by Default!,