Joining in with Google, Yahoo & recently Bing, Yandex has decided to also strip search query data from the referrer meaning that Yandex is now 100% not provided. The announcement roughly translated from Russian reads as follows:
In December last year we started an experiment to encrypt text query in the Referrer , which gradually expanded. By February, the share encrypted data has reached 30% of user requests. Time that has passed since the announcement, made ??it possible for webmasters to shift to other methods of estimating the user’s interests. From today we start encrypting referrers at 100% of the flow of requests. Statistics searches for sites in your metrics and service for webmasters still available in full.
The important bit I want to point out here is that the term encrypting does not actually mean an encrypted connection (such as an SSL connection) is established. If you go ahead and visit http://yandex.ru and run a search query you’ll notice that you do not change over to https:// – instead Yandex is literally just striping the search query information from the referrer.