It seems the forum is being visited by spammers which post messages advertising and linking to porn and SEO sites that want to sell you something.
One user (who fooled me initially by just having the link in their footer) started sending personal messages to users, advertising something about Captchas.
Those (forum) accounts are banned
and the posts deleted
when I see them.
OTOH, I (Ingix) can't and won't monitor the forum 24/7, and I can't see personal messages. So if you see messages on the forum, use the "Report to moderator" button (to be found at the end of each post on the right side). If you see multiple messages, just report once, I'll clean up everything. Just put SPAM in the text, that's enough.
If you get a personal message, at the end of it is also a button "Report to Admin". Click this, add "SPAM" as reason, then hit "Report Message". If you learn of the personal message via email forwarding, you need to go to the forum and login to report it. If you get multiple identical personal messages, report them all, as they seem to come from different user accounts.