In Terraria, every so often, there is an event called the "Blood Moon." During the Blood Moon, there are more enemies, they are meaner, and they can open doors. Bad news bears all around really. So, I barricade my doors with dirt, break out the space gun and meteor armor, and regulate. If you look at the close up view, you can see the pile of coins that zombies have dropped.
I am really enjoying this game. You should all check it out, it's only $10 on Steam. Or 6 pounds if you are in Britain Land.