Russia and the former Soviet states at its periphery have remained steadfastly immune to the charms of Facebook.  The American social network figures nowhere in a list of top 10 websites by the number of unique users in Russia, Ukraine, Belarus or the Central Asian ‘Stans. Instead, Russians and their neighbors preferVKontakte, a home-grown social network that, in addition to connecting friends and groups, also functions as a dating site and offers free streaming movies and music, much of it pirated. V Kontakte has over 100 million active users on the Russian internet, or RuNet.

That’s why the agreement announced today between Facebook and Yandex, a search engine, is a big deal. Yandex, like Google, offers a baffling array of services (pdf). It is Russia’s home page and most popular site by far. Starting today, it will start listing public posts from Facebook in search results. Comments on the posts will follow, a Yandex spokesperson told TechCrunch. For Facebook, this means greater visibility among the vast majority of Russian internet users. Think of it as free advertising on Russia’s Google.

Along with China, Russia has long been a great big hole in Facebook’s quest to enlist users from all over the world. In late 2012, Mark Zuckerberg travelled to Moscow to meet the prime minister, Dmitry Medvedev. Zuckerberg gave him a Facebook t-shirt, but that seems not to have been enough to get Russians signing up in their droves.

Facebook stills lags behind not only VKontakte but also Odnoklassniki, another popular social network. One thing Facebook does have in its favor, however, is that it tends to be used by the most affluent and urban Russians—those who speak English, have traveled or have friends abroad. It may have fewer users, but they are more valuable to marketers. Showing off those users on Yandex could help bolster Facebook’s aspirational status and help it sign up more people.

What Yandex gets from the deal is ”full access to the social network’s ‘firehose’ of public data” from Facebook users in Russia, Ukraine, Belarus, Kazakhstan, and other former Soviet countries other CIS countries, according to a press release. Yandex already has access to data from Twitter, VKontakte and LiveJournal, a blogging platform which remains popular in Russia. A partnership with Facebook will allow Yandex to broaden its understanding of social conversation and to refine its results based on what people are sharing.