High Quality Content by WIKIPEDIA articles! Information leakage happens whenever a system that is designed to be closed to an eavesdropper reveals some information to unauthorized parties nonetheless. For example, when designing an encrypted instant messaging network, a network engineer without the capacity to crack your encryption codes could see when you are transmitting messages, even if he could not read them. During the Second World War, the Japanese for a while were using secret codes such as PURPLE; even before such codes were cracked, some basic information could be extracted about the content of the messages by looking at which relay stations sent a message onwards.