On October 29, 1948, known as "Black Friday" in the American intelligence community, the Soviet Union and it's allies changed all of their codes, ciphers and communications procedures. This was a disaster because the U.S. and Britain had cracked Soviet military codes and were reading all the Soviets secret messages. At the time, it was known who tipped them off. It was an American soldier, William Weisband, who worked in the army security organization that later became the National Security Agency. At the time, Weisband was not prosecuted, because it was felt that too many still secret items would come out in court. Weisband was booted out of the army and died of natural causes in 1967. Now, details of that code breaking effort are starting to come out, but not all of them. At the end of the war, American intelligence agents obtained one of the Soviet cipher machines and, working with the British experts who had cracked the German Enigma machine, were soon reading Russian encrypted messages. Other Russian codes were cracked as well. What is left unsaid, for the moment, is which Russian ciphers were cracked after 1948. The National Security Agency has had the tightest security of any American intelligence organization, and has been most successful at keeping its secrets.