I run a Swedish site about energy drinks, along with a Swedish forum for energy drink collectors. In a tie between phpBB and Simple Machines (SMF) I chose the latter as forum software.
Since I opened the forum there has been more and forum spam attempts. Actually there have been very few spam posts, and no spam personal messages that I know of, but several spammers did register only to add links for SEO purposes in their user profile. (Note to self: set rel=”nofollow” on links in user profiles?)
The first counter-measure I added was reCAPTCHA for SMF and it has saved me quite a bit of work.
When that was not enough I found an SMF plugin for the Stop Forum Spam API. Unlike Akismet that – AFAIK – goes for the content of the spam, Stop Forum Spam simply stores IP address, user names and e-mail addresses that have been used for forum spam. When a spammer try to register on my forum they get a message (in Swedish) that an extra security check is needed, and instructions to e-mail the webmaster (that’s me). I have loads of registration attempts in the forum log, but no e-mails to webmaster… 🙂
I realize that it is not realistic to get rid of all spammers, but I’m pretty close now!