Ok so i've heard of people having a problem with having two different accounts for mine craft on one computer. The problem im having is that my younger brother had bought mine craft after I did, he made a map and started playing. then when i logged in i noticed his map on my account. so out of curiosity i got him to log into his own account and play my map. out of my surprise his was logged in as himself playing as me!!!!! will this affect my account and map if he were to ever screw around with my map. is there a way i can lock him out of the map. and can i play my single player map from any other computers? any help would be great.