Microsoft's search engine, or decision engine as it was once marketed, has had the option to encrypt search traffic for over a year. But this feature was an option and users of Bing rarely scope beyond the initial search page into the settings of the service.
Today Microsoft is announcing that sometime this summer (seems to be summer already where I am) the company will be turning on search encryption by default. Including this capability inherently will keep included query terms from showing up in the incoming traffic logs of marketers and webmasters.
For those marketers and webmasters that rely on the private information in the Bing referrer string, Microsoft will still provide limited information, but only using Microsoft's own web tools.
Read the full announcement here: Bing Moving to Encrypt Search Traffic by Default