I just checked, and these are almost all IP ranges from South Korea. So that’d be another way to slow these guys down, if we had a geolocate IP at the time of signup check, and you could block certain countries from registering, that’d be a cool plugin!
Note that they do have a handful of other country IPs mixed in there like the one from Italy, and another from NY, so I think they have a few tricks up their sleeve if they keep getting blocked based on geolocation of IPs.