As was usual in instances of this sort, the local people were told what it was and were asked to keep secret what they had seen. citation Allied investigation Despite their low success, the authorities were worried about the balloons. Source: Internet
Winston Churchill personally issued an order for their destruction into pieces no larger than a man's hand, to keep secret that the British were capable of cracking Lorenz SZ cyphers (from German rotor stream cipher machines) during the oncoming cold war. Source: Internet
Until recently Tamil Tigers managed to keep secret their very close link with Khalistan terrorists mainly the Khalistan Zindabad Font (KZF) - another banned terrorist group like the LTTE in USA and elsewhere - but not anymore. Source: Internet
Money spent on children are keep secret. Source: Internet