Even inside the egg shells, a hard boiled egg is still a perishable food, so it cannot be kept at room temperature for longer then 2 hours. Inside the refridgerator, a hard boiled egg can be kept for up to a week, but really not much longer. To best store hard boiled eggs in the fridge, store them in water (changing the water daily), or store them in a closed containter wraped in a damp paper towel. If the egg has an upleasent and foul oder then it is spoiled so throw it out. If a hard boiled egg has a green ring around the yolk that does not mean it is spoiled, it just means that it was overcooked. Another tip you can use to tell how fresh a hard boiled egg is, is by how easy it is to peel the shell. The harder to peel the shell, the fresher the egg. The easier it is to peel the shell, the older the egg is.