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 …

Ipstenu (Mika Epstein)

We’ve all had this problem: a group of spammers from <code>mail.ru</code> are registering to your blog, but you want to keep registration open. How do you kill the spammers without bothering your clientele? While you could edit your theme’s <code>functions.php</code> and block the domain, once you get past a few bad eggs, you have to escalate.
Ban Hammer helps you do that by preventing unwanted users from registering.
On a single install of WordPress, instead of using its own database table, Ban Hammer pulls from your list of prohibited emails from the Disallowed Comment Keys feature, native to WordPress. Since emails never equal IP addresses, it simply skips over and ignores them.
On a network instance, there’s a network wide setting for banned emails and domains. This means you only have one place to update and maintain your blocked list. When a listed user attempts to register, they get a customizable message that they cannot register.
For advanced documentation, including how to use on WooCommerce, please visit <a href="https://github.com/Ipstenu/ban-hammer/wiki" rel="nofollow ugc">the Ban Hammer Wiki</a>.
<ul>
<li><a href="https://github.com/Ipstenu/ban-hammer/" rel="nofollow ugc">Development</a></li>
<li><a href="https://github.com/Ipstenu/ban-hammer/wiki" rel="nofollow ugc">Wiki</a></li>
<li><a href="https://ko-fi.com/A236CEN/" rel="nofollow ugc">Donate</a></li>
</ul>
<h4>Privacy Policy</h4>
This plugin does not track data outside of what WordPress already collects. It utilizes the submitted email address to validate the domain and compares it to the list of prohibited domains and emails. No additional data is processed.
<h4>Credits</h4>
Ban Hammer is a very weird fork of <a href="http://www.joeswebtools.com/wordpress-plugins/no-disposable-email/" rel="nofollow ugc">Philippe Paquet’s No Disposable Email plugin</a>. The original plugin was a straight forward .dat file that listed all the bad emails (generally ones like mailinator that are disposable) and while Ban Hammer doesn’t do that, this would not have been possible without that which was done before.
Many thanks are due to WP-Deadbolt, for making me think about SQL and TTC for StopForumSpam integration. MASSIVE credit to Travis Hamera for the StopForumSpam/cURL fix! And then props to Helen Hou-Sandí for not using curl at all. Protip? Use <a href="http://planetozh.com/blog/2009/08/how-to-make-http-requests-with-wordpress/" rel="nofollow ugc">WP_http</a> instead!

Ban Hammer

Prevent people from registering via your disallowed comment keys.

WP-BlockYou vs Ban Hammer