The ultimate protection: require registration
The most effective method for preventing automated comment spam is simply to change your Wordpress blog settings so that only registered users can post a comment. Since the registration process is more strict (and is yet another step that spammers are unwilling or unable to complete) requiring users to register to your blog before they can comment effectively stops all spam.
You can turn this option on in the Settings > Discussion section of your Wordpress admin. Just check the box labeled “Users must be registered and logged in to comment” and you’re done.
Of course the down side of this method is it puts a serious impediment in front of users. Most people on the internet are not going to comment if they have to fill out a form first to register (internet users are inherently lazy).
So while requiring registration is certainly effective, it can also seriously reduce the amount of comments you’ll receive.
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