There are three types of spam you need to worry about
: 1 = bots spamming your forum; 2 = spiders crawling your site for email addresses; 3 = members registering with website names. The other tips to prevent spam are somewhat already known
To prevent form 1)
I have a heavily censored board, (At least I think so) and whenever someone types in a "no-no" word, they get replaced with 'I love mysite.com, it is a great place..."). So even if bots register to spam, and post a message, there is a big chance it will be filtered out.
vbseo also helps with filtering out certain types of registrations.
To prevent form 2)
Place this button on your forum ->
It gives spiders who crawl your site for email addresses bogus emails.
To prevent form 3)
Go to your admincp and look at options panel, I believe it is the registration option or somethign related to users and look for where it ask you about user names or characters that are prohibited or something close to this -- to be used as user names.
Then, choose whether you want to prevent members from registering with
www.look.com or whatever.
On number 3 above, I just choose to prevent users from registering with a period in their user names ----> . <---- But I allow www and http
Oh yeah, I'm not sure about your forum, but my forum is in an industry that is often times filled with scammers, hackers, phishers, and the like, so I also blocked executable files from being linked to my forum.
If you link
www.mysite.com/clickhere.exe on my forum, the .exe will be replaced with the censorship message I have in place.
Also, if you get members that sign up to get signatures, make them do work and earn the signature, so that they don't spam your forum with their signatures.
For my forum it takes 50 "quality" post to be able to use a signature, earn a badge, and send private messages.
Also, you might want to look at modifications that make banning easier, as well as prevent certain "troublesome email addresses from signing up.
Oh yes, one last thing, turn off all if not most features for guest.
Install the hack that allows you to resolve an ip hidden behind a proxy.
And tell your members/guest that you can find their ips and will not hesitate to turn them into the appropriate authorities if need be.
I think a privacy statement covers that.