Comment blacklisting works well, but what if you actually want to stop someone from even reading your blog? This plugin will take care of that for you.
It uses .htaccess file modifications to deny access to your blog from particular IP addresses (Deny from) and then follows up with an ErrorDocument 403 redirect to a URL of your choice. It doesn’t hook into WordPress, which makes it a lot faster due to no database or PHP calls.

WP-BlockYou

A plugin that can be used to block or "ban" users via their IP address from viewing your blog, and then redirecting them to a URL of your ch …

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Spam Check for Asgaros helps you keep your forum clean from spam.
When a user creates a new post or topic in Asgaros Forum, the content is scanned for a list of blacklisted terms that you define. If any are found, the submission is blocked, and the user can optionally be banned.
Features: 
– Check both new post (reply) and new topic content for spam keywords 
– Manage blacklist terms easily in Settings > Spam Check for Asgaros 
– Choose whether to automatically ban users on spam detection 
– Customise the error message when spam was detected 
– Lightweight and fast

Spam Check for Asgaros

A simple and configurable spam filter for the Asgaros Forum plugin. Automatically detects blacklisted terms in posts and optionally bans spammers.

WP-BlockYou vs Spam Check for Asgaros