It enables you to view the comments first and then approve it to be shown publicly.You can control WordPress comment Spam or unrelated comments by editing or trashing it.
Use Plugin – WP-Recaptcha
This is My favorite and a must have for sites accepting guest blogs and comments.It easily installs google reCAPTCHA in your site which nullifies the automated abuse i.e. user have to spend time and manually spam your site with comments.This also prevents spammed user creation if you have a user registration page for contributors.After installing all you have to do is get your public and private API keys from http://www.google.com/recaptcha/whyrecaptcha and put those in your plugin setting page.You can download the WP-Recaptcha plugin here.
Use Plugin – Akismet
Akismet Plugin protects your blog from all sorts of comment spam.All you need is to generate a wordpress key after activating the plugin. One issue could be a genuine comment being marked as spam and hence hides in the list of spam comment list.If the list becomes lengthy then it is time taking to find and undo the spammed comment. Download plugin and get the key here.
Comment Using Comment Luv
Comment Luv is an awesome plugin which encourage bloggers to comment with an option to share their posts in the comment body of other blogs.Thus earning a valuable link to your post and blog.Since comment luv is used only by bloggers with valid identity, the comments are usually not spam.
Only registered Users Can Comment
Go to Settings -> Discussion . Go through the “Other Comment settings”. Enable users to comment only after registration.This could be helpful in preventing spam but it also reduces the number of comments as the process of registration could be found to be time taking for many.
Wp-ban WordPress plug-in makes it possible for you to see the IP addresses of anyone who is visiting your blog, and ban users who is spreading irrelevant or spam comments.
Use facebook Comment
Since facebook users are more valid and the chances of a facebook user involved in spam is less.You need to create a facebook app and install out of many available plugins to enable facebook comment on your blog.You may then choose to turn off the wordpress comment completely and enable comment using facebook only.
By setting up a link restriction on comment e.g. limit to one link per comment will reduce the number of spams as they target to achieve maximum number of links by spamming.
Closing Comments for Older post
Usually In wordpress comment spam takes place in older articles where spammers try and sneak into. So based on popularity and nature of the post, you may wish to turn off the comments completely. You may also auto turn off all articles which are for e.g. 15 days old by going to comment setting in the setting->discussion tab of wordpress dashboard.
Turn off trackbacks
Trackbacks are those incoming links that you see in the wordpress dashboard.Those are links from google blog search.If you believe you are not getting much resource out of it then turn it off as It could also be a source of spammed links.