the worlds are corrupted

When they enter the game folder and change the name to your world folder, the world gets corrupted and appears with the 0 seed, and also creates a different folder that says that Minecraft has a number on the side and when you enter that world. It is raining and in survival and everything is different from the original world, even if the world folder has a different number always the seed is 0.

 

this happens in version 1.4.1.0