1. WP-reCAPTCHA
reCAPTCHA is an anti-spam method originating from Carnegie Mellon University which uses CAPTCHAs in a genius way. Instead of randomly generating useless characters which users grow tired of continuosly typing in, risking the possibility that spammers will eventually write sophisticated spam bots which use OCR libraries to read the characters, reCAPTCHA uses a different approach.
2. Akismet
Akismet checks your comments against the Akismet web service to see if they look like spam or not and lets you review the spam it catches under your blog’s “Comments” admin screen.
3. Ntz Antispam
A completely rewrite for the old plugin. The plugin works now in a different way. Instead of waiting for robots to fill a field, I decided to go to another route: use a nonce key and a time stamp.
4. Awebsome! Comment Author Mail Validation
Adds a new comment validation method in the “Before a comment appears” Discussion subsection panel.
5. SI CAPTCHA Anti-Spam
Adds CAPTCHA anti-spam methods to WordPress on the comment form, registration form, login, or all. Also is fully WP, WPMU, and BuddyPress compatible.
6. AVH First Defense Against Spam
The AVH First Defense Against Spam plugin gives you the ability to block spammers before any content is served by identifying them at the Project Honey Pot, a local blacklist or the local IP cache. Visitors trying to post a comment are checked at stopforumspam.com. Stop Forum Spam is not used to check before content is served due to the amount of requests, which overloads their infrastructure.
7. Greg’s Comment Length Limiter
This plugin provides a configurable limit on the length of comments left in the comment form, with a character countdown displayed for the user and dynamically updated with each keypress.
8. Stop Spammer Registrations Plugin
The Stop Spammers Plugin Plugin Accesses the StopForumSpam.com db to check emails, username and IP before a user can register. The StopForumSpam database contains over a million spammer emails, User Names and IPs, and is updated daily.
The plugin validates Email, IP and User name against the StopForumSpam.com db. It denies login attempts, such as spammers trying to guess passwords or spammers trying to create login ids. It also stops spammers who try to add comments with a spammer email or ip addresses.
9. Animal Captcha
Animal Captcha is a lightweight plugin for WordPress that adds a captcha control on comments and register with a nice picture of an animal than any man knows, and yet a robot is unable to identify. It’s nice, comfortable and very safe. Languages: English, Spanish, German, French and Portuguese
10. Comments Capcha Box
This plugin creates a capcha box before your submit button in the comments section to prevent all that unwanted spam.
11. Block Spam By Math Reloaded
This plugin protects WordPress 3.x (single/multisite) registration, login and comment forms from spambots by adding a simple math question to it (“what is 4+3 ?”). It also includes support for Buddypress. This is a proven approach to dramatically decrease your amount of spam. This plugin is based on the Block-Spam-By-Math plugin created by Alexander Grau.
12. TrollGuard
TrollGuard is a free WordPress plugin that protects your blog from spam comments. It learns to filter out spam from your training. After a short while it has adapted to your personal blog and will accurately detect incoming spam. TrollGuard is developed on top of uClassify which is a free web service for text classification.
13. CryptX
No more SPAM by spiders scanning you site for email adresses. With CryptX you can hide all your email adresses, with and without a mailto-link, by con
14. NuCaptcha WordPress Plugin
Publishers have a choice between old style, static Captcha security and the NuCaptcha platform; a multi purpose product which provides industry leading security combined with brand messaging, advertising and unique user engagement.
15. Conditional CAPTCHA for WordPress
Asks commenters to complete a simple CAPTCHA if a spam detection plugin thinks their comment is spam. Currently supports Akismet and TypePad AntiSpam.
16. Chronological Spam Removal
This plugin will delete comments that have too many links. Spam can also be deleted if it has a url in the author url field. This is handy if you don’t have a author url form field in your comment form, and bots are submitting without using your form. Finally, spam can be deleted if there are any non US-en keyboard characters in any comment row. I don’t expect any foreign language characters on my blog, and while I know this setting may be a little harsh, it’s a spammy world out there, and sometimes ya gotta do what ya gotta do.
17. NoSpamNX
There have been many new good ideas of fighting automated Spam in WordPress. Most of these Plugins (like the antecessor of NoSpamNX: Yawasp) change the name of one (or more) of your comment field. On the one hand, this is indeed more effective, but on the other hand, this goes to the expense of compatibility. Therefore, NoSpamNX does not change any of your comment fields, but still claims to be very effective.
18. Antispam Bee
Protects your blog from spam by replacing the comment field. It’s easy to use and extremely effective. Really!
