Materialising World Exploit?

Today I was playing on server and the following happened (image url below)

http://www.glowfoto.com/static_image/16-070353L/2684/jpg/05/2010/img5/glowfoto

Random ragdoll models appeared with a skybox as and effect,this causes people to crash out because of low FPS.The thing is it wasnt admins and the server had to be restarted in order to remove those things.Someone said its an exploit in meterialising the word and the ragdoll models were an exploit too where the models aren’t actually npc’s they are just models, but they still count as npcs.

I was wondering if this was true and if there is anyway to prevent it in future.

what I see are just a few props / effects…

And thats what I am talking about.The effects appeared there randomly and the heavy model too.The whole server was like that had multiple models and effects around.(sorry for the bad image)

Seems that someone is just joking around with advanced dupe…

Adv Dupe is disabled on that server.And noone can spawn effects,npcs or ragdolls.