The National Security Agency may be known for its stealthy eavesdropping techniques, but it’s going public with advice for how to train a new generation to defend against computer threats. Representatives from the usually secretive agency appeared at a SANS Institute event here to divulge “lessons learned” from their latest cyberdefense exercise. The exercise, which took place over four days in April, pitted students from the five U.S. military academies and the Air Force’s postgraduate technology school against “bad guys” at NSA headquarters. NSA representatives said they hoped the informal briefing would provide a wake-up call to all network managers, both inside and outside the government.