Forum Post: Implement an algorithm to remove copy/pasted messages

Moderators and forum programmers, can you please implement an algorithm which would make it impossible for people to copy/paste their messages and use this board for advertising their same idea or link over and over again. Just check if 50% of the content matches with another post in the database. If it does, make it viewable only to the spammer so he or she believes it has been posted, but hide it for the rest of us. Thank you.