I used to get these too so there is a setting in the ACP to not allow any registrations from certain countries/areas. So if you don't want to allow anybody from Russia to attempt to register for your forum do this...
AdminCP -> Members -> Content Moderation -> Spam Prevention -> Geolocation Settings -> +Add button ->Scroll down to "Russian Federation" -> "Do not allow user to register at all" -> Save
This stopped a lot of it for me, hope it works for you