Comment spam is a fact of life if you have a blog.To fight with spammer there are some handy WordPress plugin solution to help you.
[1]. Akismet
Akismet uses a unique algorithm combined with a community-created database to “learn” which comments are comment spam and which are legitimate.This plugin costs $5 a month if you make any money from your site, such as through an affiliate link, ad, or paid service.
[2]. WP-reCAPTCHA
reCAPTCHA is probably the most popular and widely accepted CAPTCHA systems by both end-users and site-owners. It is used by such sites prominent sites as Facebook, Twitter etc.
If the user has trouble reading the CAPTCHA challenge, he or she has the option of requesting a new one. If this does not help, there is also an audio challenge which users may use.
[3]. Stop Spam by referrer requests
Use this .htaccess code on your WordPress default .htaccess file to prevent spammers posting on your blog.
[php]
RewriteEngine On
RewriteCond %{REQUEST_METHOD} POST
RewriteCond %{REQUEST_URI} .wp-comments-post.php*
RewriteCond %{HTTP_REFERER} !.*yourblog.com.* [OR]
RewriteCond %{HTTP_USER_AGENT} ^$
RewriteRule (.*) ^http://%{REMOTE_ADDR}/$ [R=301,L]
[/php]
And replace yourblog.com with your own website URL when you implement it.
Source: How to deny comment posting to no referrer requests
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