Since i run several successful anonymous imageboards, one of the ways to prevent spam is to have a sort of spam list (i would say blacklist) of all the domains url’s that are not able to be posted on the board (since one of the main reasons to spam the boards is to post links to fishing or illegal sites), this way this prevents them being posted by bots altogether.
So its an essential tool to have a clean board and to keep things clean, even if later on more automated tools like akismet or defensio are included, this is still a nice clean and fast way to keep most spam or idiotic posts from the site, so the file is a simple spam.txt file on the root of the site, one domain/site per line, this of course is most useful to other imageboard hosts that use the same system (wakaba or kusaba clone software), so here is our very own custom spam.txt list hehehe for free yayy 1131 domains (i’m actually thinking about making our own system, so anyone can add links and have the latest version for their board so their system is always protected heheheh)
UPDATE (from tentakle and neechan):
Uhh since the last post we have added a bunch more, so there ya go an updated spam.txt this new list has 1372 domains that are/were used in spam posting on imageboards, the old link as well hehehe, you can use something like WinMerge or TextOpus to help merge your existing spam file with my awesome one ^^