Looking for help with Spam Prevention script.

I have a short script set up that times out users who post a certain amount of messages in a certain allotted time period.

But what I'm currently looking for is something that prevents users from typing the same message repeatedly without a time period (it needs to be the same message or else it would just time them out for typing a few random messages).

Also, if you have any idea of a script that would stop spam bots (the kind that log in multiple users and each user repeats the message sent by the first) that would be insanely helpful.

Thank you :)