Hey, that thread helped me understanding the logic to prevent the refresh duplicates, but in the it still not bullet proof? Wouldn't it be really easy for someone to just add a random generated session id and tag it on the session_id parameter, and keep making form requests to your validation script. The validation script will always receive different generated sessions, thus making it really easy to flood your directory?

Perhaps, add a IP field and only allow 5 max request per? But then someone can trick the IP or perhaps connect to a list of proxies and take turns 1 by 1?

Theres really no reliable way is there?