I think the main source may be in Russia; or that was with libgen.

But I could be wrong.

I am more surprised to see that there are so few alternatives to it. Or perhaps I am unaware of them but after Facebook and co declared war on libgen, and libgen going down, there were surprisingly few alternatives. Anna was one of the few. I still don't know what happened with libgen, but since the attack it really is kind of semi-gone.