How to stop crackers / hackers to post comments on drupal site.

Hi Guys,

How to stop crackers / hackers to post comments on my site? I am using drupal higher version.
I delete almost 100 comments everyday :(
I am looking for a solution. Please help me. I've searched but unable to find an answer!

Thanks in advance.
Regards,
MS

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A Solution!

Thank you all for your time and feedback. I've found a solution. Please read my another blog post Stop spam on drupal - A Solution. I am almost 100% spam free I mean my site :)

Thanks again
Regards,
MS