Guy has chest full of diamond, says he "duped" it??

I just started a minecraft server today and someone on my server had an entire chest FULL of diamond. When I asked him how he said he duped it. He also showed me this video:


Obviously this shouldn't be happening on my server. How can I stop this from ever happening again? Is there a plugin that will prevent this?

 

Have you updated to latest RB?

http://dl.bukkit.org/downloads/craftbukkit/view/01119_1.2.5-R3.0/

They have fixed the dupe bug with nodus in it.

 

I use creeperhost.net to run my server. I'm not even sure how to upgrade

 

You should contact them. Also (just my oppinion) if I were you I would get rid of that player, having nodus in the first place can't be a good sign unless u have a "everything goes" server I guess.

Just my oppinion. Your host should have some kind of support system, too.