We've been hit over the last couple of weeks by over 300 registrations who send a single private message to a member inviting them to visit a bitly.com link to fill a survey or enter a promotion. I haven't clicked it, so I don't know where it goes.
There are some attributes of the...
Block registration / new thread post based on ip to country detection (provided by maxmind's geoip).
Use blacklisting / whitelisting method.
Allow empty country / not.
Latest test was using XF 1.4.6
This product is only tested using IPv4.
I have not tested using IPv6.