Bing now appears to be supporting secure search through the https://www.bing.com address. Previously, trying to use this address generated an error.
If you conduct a search on Bing, while on the HTTPS URL, it will remain HTTPS and keep your searches secure. This is a new feature Bing quietly started supporting over the weekend.
Cyrus Shepard tested to see if the query data would pass from Bing SSL search to Google Analytics. It is known that the standard protocol on the web is to not pass query referrer data from HTTPS to non-HTTPS, but from HTTPs to HTTPs, it should pass.
I am not sure if Bing SSL will pass query data from HTTPS to HTTPS but it definitely should not pass from Bing SSL to a non-HTTPS site.
Microsoft has not announced any plans for Bing to go SSL yet but this may be a sign that it will come in the near future.
Postscript: A Microsoft spokesperson responded to our request for a comment, below is their response but we do have several follow up questions:
At Bing we are always experimenting to improve the overall search experience and understand that people want choices in how they protect their privacy online. By providing optional access to Bing.com via HTTPS, we are giving everyone the ability to decide how they use Bing while also being thoughtful about how we implement this functionality.
Postscript #2: I asked Bing how will they handle passing referrer and query data to webmasters. They sent me this statement:
At this time we are still evolving our rollout of HTTPS at Bing. As we continue to develop our implementation, we will keep the SEO/SEM community needs top of mind and balance them with consumer privacy and security concerns.