Akismet is a proven way to prevent comment spam in wordpress powered blogs. It does a great job of sifting spam comments and redirecting them to the spam folder.
There is still a problem with this. Though spam get redirected to the appropriate folder but it unnecessarily clogs our MYSQL database. Moreover there is always a chance that among the hundreds of spam comments there is one good comment and unknowingly you might end up deleting that good comment as well, while cleaning up the folder.
I did some analysis on my spam comments (wordpress dashboard > comments > spam) and found that they mostly originate from 2-3 common IP’s. If I can get some way to automatically delete comments coming through those IP’s my problem would be partially solved(other spammers would still be there…grrr).
Here is a simple SQL script I wrote to do this:
[source:sql]
DELETE FROM `wp_comments`
where `comment_author_IP` = ‘66.159.18.9’ OR
`comment_author_IP` = ‘84.19.188.218’;
[/source]
Keep on adding the spammers IP’s that you see from your wordpress dashboard.
Now you can set up a cron job that runs every night or every week or every fortnight (depending on your requrements). All your spam comments would get deleted automatically at a given interval.
Gozar!
Ankur Jain is a Software Engineer in Test Automation. After a 5 years stint with Accenture and Oracle, he started his eLearning company. A long-time blogger and proud owner of the "Learn" series of websites. 
Nice idea to block spam without any false positives and extra plugins. I love the fact that its very light!
Thanks Mr.I
Simple..but genius 🙂 Nice post. Spammers mostly use the same ip as many of them uses anonymous posting service to send spam.