60 MINUTES presents a special hour with two stories featuring hidden cameras that capture conmen at work. 21st CENTURY SNAKE OIL - 60 MINUTES hidden cameras expose medical conmen who prey on dying victims by using pitches that capitalize on the promise of stem cells to cure almost any disease. Scott Pelley reports. David Gelber, Sam Hornblower and Michael Radutzky are the producers. THIS IS A DOUBLE-LENGTH SEGMENT STEALING AMERICA'S SECRETS - 60 MINUTES has obtained an FBI videotape showing a Defense Department employee selling secrets to a Chinese spy that offers a rare glimpse into the secretive world of espionage and illustrates how China's spying may pose the biggest espionage threat to the U.S.. Scott Pelley reports. Henry Schuster is the producer.