You don't need to hack Yandex. The entire monorepostory is synced on every intern's laptop, and you can do whatever your want with the files. I always wondered how it hasn't been leaked before to be honest.
If they're still using Subversion, why would that be? Subversion lets you check out just part of a repo. (Then again, interns, I guess.)
2. Subversion lets you check out portions of your repository.
3. Subversion working copy does not have all regions history. Just a snapshot of the checked out revision.
So at least Subversion would have allowed them to limit the amount of leaked data + no revision history leaked.