A lot of people are currently spawning Wither bosses near spawn, or near/in people’s houses. Withers are quite destructive and there have been several incidents of them being used to grief. So until further notice:

WITHERS ARE NOW BANNED IN THE OVERWORLD.

Building a Wither in the Overworld is now considered griefing and will result in a 7 day ban.

If you want to spawn Withers, go to the Nether and do it there. We may set up a special Wither-fighting arena in the Overworld later on for you to fight them in, but until then, building Withers ANYWHERE in the Overworld is banned.

— TerrorBite