Severe Posting Spam

I need a way to stop posting spam from happening.

[Gizmare]

Anyone have any ideas on how to prevent posting spam. One of our websites was just hit with about 800 posts to our contest entry form from a single persons IP. I had my ISP block access from the IP to give relief to the recipient temporarily. Any ideas would be helpful.

Thanks

[Quinn]

What about a dynamically generated image with a character code similar to Altavista's security ransom code?

Not too high tech, but should cut down on the auto submitters.

[Gizmare]

Thanks not a bad idea at all.

[ggrot]

Block user agents that aren't browsers for starters. VB has a very specific one that is often the source of troublemakers: "Microsoft Url Control" followed by a version number.

Also if you have enough control over the forum scripts, make sure all submissions are done through 'post' not 'get' and check server side that the submissions are indeed post. People writing software to send form data can't generally figure out how to 'post' as easily as appending to the url.

Finally, add a timing system into the scripts so that a single ip cannot post more than say 5 messages per 5 minutes or something along those lines. This will slow them down and reduce the work required in cleaning the stuff up.

These 3 combined will really go a great deal in reducing automated types of spamming you are referring to.