President Truman was never told of the Venona decryptions. It gives one pause to think now that all Truman ever "learned" about Communist espionage came from the hearings of the House Un-American Activities Committee, the speeches of Senator Joseph R. McCarthy, and the like.
This is amazing to me. It is scandalous enough that the American public was never told about the Venona decryptions. The Russians were apparently tipped off in 1948, and by 1950 the NSA uncovered the spy who told the Russians. After 1948, no more of the Russian communications were decrypted by the US. So why the secrecy, if the Russians knew and nothing more was being decrypted? And why wasn't this important enough to tell the President of the USA?