A new trend in spam is to duplicate legit comments from your readers to hopefully pass spam filters. Spammers post content that was previously approved on your site, but with their own name and URL. This plugin prevents this.
Installation is, as usual :
- Upload files to your
/wp-content/plugins/ directory (preserve sub-directory structure if applicable)
- Activate the plugin through the 'Plugins' menu in WordPress
- Refer to the official plugin page for documentation, usage and tips