How do I protect my forum against spam?

Question

I have a forum on a website I master, which gets a daily dose of pron spam. Currently I delete the spam and block the IP. But this does not work very well. The list of block

Answer 1

The spams may be by bots or humans - bots are more likely.

To stop the bots, put in a hidden field populated by Javascript - there is a 99.5% chance that a standard, stupid bot that isn't customised to your site will fail to fill that in.

If they fail to fill it in correctly, give them a message that Javascript is required or something, and give them an opportunity to post some other way (e.g. with a captcha or registration). That way anonymous users who aren't spambots can (mostly) still post with no problems, and most spambots (which haven't been tailored for your specific site) won't.

Don't bother blacklisting IP addresses or using third party blacklists, that will just generate false positives. Almost all bots use the same IP addresses as (some) legitimate users.

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Another trick is to put in a text field with a plausible sounding name, which is made difficult to see with CSS - anyone filling this field in with anything is considered to be a bot.