spam prevention - Prevent user from Sending Duplicate messages using PHP -

Can a good PHP function suggest a method to stop the user from sending scripts, scripts, or duplicate messages?

The scenario here is one of my community websites, members can send a second message. Then some spammers from Africa contacted all the members by sending duplicate paste messages. How can I stop it?

I have noticed that some websites apply the same functionality when a user sends 3 messages and the website finds that these 3 messages are duplicate / similar, it warns the user against spamming.

Is anyone aware of a function or script that I could use? Thank you in advance.

The first thing to do is define the rule, for example, if you believe that you have three messages If properly sent, then bypassing the system can be very easy.

A suggestion the way I did something like this - this function

  $ var_1 = 'PHP is large'; $ Var_2 = 'with MySQL'; Identical_text ($ var_1, $ var_2, $ percent); Echo per cent; // 27.272727272727Same_text ($ var_2, $ var_1, $ percent); Echo per cent; // 18.181818181818  

Then check the user's history, if you have 80% or more of the previous 3 messages, then you block the user.