The main solutions we have today are IP ban + VPN blocking using a database of known VPN subnets and adding them all to the firewall, and a similar fingerprinting technique which scans their folder structure of certain system folders.
The main solutions we have today are IP ban + VPN blocking using a database of known VPN subnets and adding them all to the firewall, and a similar fingerprinting technique which scans their folder structure of certain system folders.
Regular IPs can post freely
VPN or mobile IPs (blacklisted) must pay for a key ($20/year) that allows posting from blacklisted IPs. Key is good for posting from one blacklisted IP, locked for 30 minutes, so users cannot share keys. That way, you can ban the user by their key, if their IP is public.
It's not a perfect solution but it seems to be the best they've found for such a situation so far.
EDIT: Well, I guess the tribe has spoken. Pretty surprising. I think y'all are just assuming you'll always be the ones with the "good" IPs...
On some Japanese BBSes, spammers tend to use non-Japanese IPs or data center IPs. A good chunk of the spam goes away by blocking non-Japan IPs (easy to do with BGP data) and disallowing data center IPs (these often host VPNs, scrapers, etc.) from posting.
Posting from overseas thus costs money or is not possible. The trade-off is 1-100 extra users or significantly reduced spam for little effort. It's not surprising that most website operators choose the latter.
I also know of a file uploader that recently had to block overseas IPs due to such IPs repeatedly uploading illegal content. This is an example of a few bad actors ruining things for everyone.