lelandf

Stop Signup Spam will prevent user registration of anyone trying to sign up with an the email address or IP address that has been reported to <a href="http://stopforumspam.com/" rel="nofollow ugc">Stop Forum Spam</a>.
Contrary to what the name implies, Stop Forum Spam can be used with any web service, not just forums.
At this time, Stop Signup Spam integrates with:
<ul>
<li>The core WordPress registration form</li>
<li>Restrict Content Pro</li>
<li>MemberPress</li>
<li>Give</li>
</ul>
By installing this plugin, you consent to an API call sent from your WordPress site to Stop Forum Spam after every attempted user registration. The API call includes the user’s email address and IP address.
It is a similar concept to <a href="https://wordpress.org/plugins/akismet/" rel="ugc">Akismet</a>, except instead of checking for blog comment spam, it checks for user signup spam.
Unlike Akismet, no API key is required to query Stop Forum Spam’s database. Partly because of this, I decided not to include a settings page in the Stop Signup Spam plugin. Just activate and you are all set.
The plugin does not log any user registration info. Any data sent to Stop Forum Spam would fall under their <a href="https://www.stopforumspam.com/privacy" rel="nofollow ugc">privacy policy</a>.
Please note that Stop Forum Spam is a third-party service that I have no affiliation with. I just found it, could not find any existing WordPress plugins that worked with it, and built one myself.
It has helped me cut down on signup spam on a free membership site that I run, and I hope it will help you do the same.

Stop Signup Spam

Check user registration info against the Stop Forum Spam database before allowing registration

Automattic

Donncha O Caoimh (a11n)

This plugin adds a stylesheet or image to your blog’s html source code. When a browser loads that stylesheet or image a cookie is dropped. If that user then leaves a comment the cookie is checked. If it doesn’t exist the comment is marked as spam. 
The plugin can also check how long it took a user to enter a comment. If it’s too fast it’s probably a spam bot. How fast can a legitimate user enter their name, email, web address and enter a well thought out comment?
For the adventurous, add these lines to your .htaccess and it will block spam attempts before they ever get to WordPress. Replace the Xs with the cookie that was set in your browser after viewing your blog. You can also find the cookie value by examining the page source code and looking for “css.php?k=XXXXXXXXXXXXXXXXXXX”. Make sure the lines go above the standard WordPress rules.
<pre><code> RewriteCond %{HTTP_COOKIE} !^.*XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.*$
 RewriteRule ^wp-comments-post.php - [F,L]
</code></pre>
If you use WordPress MU, replace wp-comments-post.php above with wp-signup.php to block spam signups.
<pre><code> RewriteCond %{HTTP_COOKIE} !^.*XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.*$
 RewriteRule ^wp-signup.php - [F,L]
</code></pre>

Cookies for Comments

If you don't use any other spam filter plugins, then you can rely on this to stop spam comments for sure!

Must have, if you don't use any other spam filters!

I'd been getting a dozen spams a day on two of my sites. We installed "Stop Spam Comments" on one and "Cookies for Comments" on the other. Both worked perfectly. No more spam. Thanks!



very easy and no more spam!

Sets a cookie on a random URL that is then checked when a comment is posted. If the cookie is missing the comment is marked as spam.

Stop Signup Spam vs Cookies for Comments