After a 5 year hiatus I came back to SMF.
I noticed that you are still using outdated visual verification.
Set to medium I am getting 20 to 50 false accounts a week.
If I set it to extreme I get around 10 false accounts a week.
Also when set to extreme, some of my friends can't read the captcha, but the bots can!
I did notice that you have an Akismet plugin. This is great for stopping new topic spam but does not stop reply spam.
I would think that with all the thought that went into SMF, security would be a priority?
take a look at http://wiki.simplemachines.org/smf/Spam_-_my_forum_is_flooded_with_spam,_what_can_I_do
also this is not a security issue, it is a spam issue. there are some improvements in SMF 2.1 already.
Welcome back ;)
Security is a priority for us. SPAM isn't exactly a security issue but instead an hassle.
You have the most efficient tool for preventing bots: Questions and answers. We've been telling this for ages, Q&A is the way to go.
If you still require visual verification, you can, eg, integrate reCaptcha --> http://custom.simplemachines.org/mods/index.php?mod=1044
Or use a different visual verification for free, eg:
http://custom.simplemachines.org/mods/index.php?mod=3824
http://custom.simplemachines.org/mods/index.php?mod=2839
A paid option which seems to work pretty good, based on the reviews: http://custom.simplemachines.org/mods/index.php?mod=3851
edit: ninja'd :P