Where did all the HTTP referrers go?

“Good (and bad news): the general consensus in the web developer community is that any and every website should be HTTPS by default. Why? HTTP by itself isn’t encrypted, leaving it open to eavesdropping, message tampering, and man-in-the-middle attacks. HTTPS, if you use it consistently, prevents these issues.

So how can that possibly be bad news? HTTPS is confusing one of the core metadata tools of the Internet: HTTP Referrers. HTTP Referrers disappear when going from HTTPS to HTTP, but, more worryingly, sensitive HTTPS Referrers still get carried when going from HTTPS to HTTPS. Most secure applications aren’t aware of where their HTTP Referrers do or don’t go. Don’t worry though: there’s hope. Or at lest meta hope…”

http://smerity.com/articles/2013/where_did_all_the_http_referrers_go.html