Amanda &amp; Steve

Is this the ultimate in automated ‘bot Spam Killers?
Spam is the bane of WordPress admin’s lives; auto-generated Spam can bypass unset hidden fields from the WordPress comment page by directly submitting the comment to WordPress.
This plugin does two things:
<ul>
<li>Removes the ‘Comment Author URL’ field from the WordPress comments form; for most non-technical blogs this optional field is irrelevant.</li>
<li>Kills WP (hey that saves some CPU cycles) if a comment is submitted which contains a Comment Author URL.</li>
</ul>
Website spam ‘bots have two aims, firstly they populate spam links within the main body of a spam comment, and the spam ‘bot also includes the spam destination in the Comment Author URL of the comment field.
We put together this little plugin as despite running two other anti-spam plugins + Google Captcha, ‘bot spam was still getting through. This was resulting in an hour or so each week weeding out the real comments that had fallen into the spam bucket due to the real commenter failing to complete the Google Captcha correctly. We also noticed that real user comments reduced with Google Captcha in place.
We don’t need to stand for this any longer; say goodbye to Comment Author URL Spam and save CPU cycles!

TMD Spam Killer

Hides the 'Comment Website URL' field, kills WP if a spam 'bot submits a comment which includes a Comment Author URL.

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.

TMD Spam Killer vs Cookies for Comments