Preventing Spammers from Commenting on your WordPress Blog
1 – Every new WordPress blog comes with an awesome anti-spam plugin called Akismet pre-installed. Make sure you activate it because it will filter out the vast majority of SPAM comments that are left on your blog posts.
If you uninstalled this plugin because you didn’t know what it was for, it's recommend that you reinstall it and activate it right away.
Simply click Plugins>Add New and search for Akismet.
2 – Moderate the comments that are left on your posts so you can manually weed out any SPAM comments that manage to make it through Akismet’s filter.
Click Settings>Discussion and then check the box beside Comment must be manually approved.
Click the Save Changes button at the bottom of the page to save the change.
Note: You can always select Comment author must have a previously approved comment but that can be risky. Some devious spammers will leave a legitimate comment the first time, then return again and again to leave SPAM comments now that their comments are being approved automatically.