Pecorino must be kept in the fridge or in a cool place e.g. cellar, you should put a plastic film on the part where it is cut and maybe wrap it in a cotton cloth (tea towel or rag). If when you go to cut it you see that there is a little bit of mold, do not be alarmed it did not go bad and it is normal, just remove the first slice and the pecorino cheese can be eaten safely.