Kasuga

Tiny Comment Spam Blocker is a lightweight yet powerful plugin designed to protect your WordPress comments from spam. It employs five different techniques to detect and block unwanted comments:
<ol>
<li>Nonce Verification – Ensures that the comment form submission is genuine.</li>
<li>Submission Time Check – Blocks comments submitted too quickly to prevent bots.</li>
<li>Honeypot Field – Hidden field that traps automated spam bots.</li>
<li>User Agent Validation – Detects suspicious User-Agent strings and blocks them.</li>
<li>Forbidden Word Filtering – Blocks submissions containing words or phrases from a configurable list within the comment body, email address, or IP address.</li>
</ol>
These filters are applied in order: if a comment passes the first check, it proceeds to the second, and so on, until all checks are applied or the comment is blocked.
Additional features:
<ul>
<li>Option to log detected spam in a local log file (up to 1.0 MB).</li>
<li>Optional email notifications when spam is detected.</li>
<li>Easy settings page in the WordPress admin panel.</li>
</ul>
<h3>Settings</h3>
The plugin provides the following settings in the WordPress admin panel:
<ul>
<li>Enable Spam Protection – Toggle the spam protection on or off. When disabled, all anti-spam checks are skipped.</li>
<li>Save Spam Detection Log – Enable or disable logging of detected spam. Logs are saved in a local file up to 1.0 MB within the WordPress uploads directory.</li>
<li>Notification Email Address – Enter an email address to receive notifications when spam is detected. Leave blank to disable email notifications.</li>
<li>Minimum Submission Time (seconds) – Set the minimum allowed time between loading the comment form and submitting a comment. Comments submitted faster than this threshold are considered spam.</li>
<li>Forbidden Words List – Enter one forbidden word, phrase, or IP address per line. Submissions containing these entries in the comment body, email address, or IP address will be blocked. Case is insensitive.
<ul>
<li>Example: 
viagra 
online pharmacy 
spam@email.com 
164.138.205.72</li>
</ul>
</li>
</ul>
<h3>Arbitrary Section</h3>
This plugin is designed to be lightweight and fast, ensuring minimal impact on site performance while providing robust protection against comment spam.

Tiny Comment Spam Blocker

A simple and lightweight yet rock-solid plugin that blocks comment spam using multiple automatic detection methods.

wpdebuglog

This is a highly powerful contact form 7 anti-spam add-on. It is introducing a new hidden field and check that one value is correct or not.
<h4>Features of Contact Form 7 Honeypot Plus</h4>
<ul>
<li>No configuration is needed</li>
<li>Better anti-spam functionality</li>
<li>No need any ugly captcha.</li>
</ul>

Contact Form 7 Honeypot Plus

Nice plugin

Contact Form 7 Honeypot Plus - Adds honeypot plus anti-spam functionality to Contact Form 7 forms.

Tiny Comment Spam Blocker vs Contact Form 7 Honeypot Plus