Take it easy, "banning" is not a solution.
With european ISP policy (dynamic) and user mistake or wrong behaviour by inadvertence the site is quickly inaccessible to many people.

Also. IP proxy switch is common on session hijack. And you know that Herve, as we have seen that together. It can also be used as a strategy to "isolate" a site or "break it" (i.e last time frxoops.org was hacked).

Finally, it send you back to Xoops Dev Team and core task.