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A guy (G) follows a millionaire (M) to a bank vault which automatically opens when its security system hears the key word "moonshine" uttered by the voice of M. Before they enter the vault room there are guards who search G for any technical equipment or any form of recording on some memory device. They find that he has a tape recorder, and inform M about their finding. M says, "That's OK when I am here, but never let anyone in here alone carrying such things."

When inside the vault room M utters the key word "moonshine" and the valut opens. When M uttered the key word, G records him. M sees that and says, "That's OK, you can record me saying that, and you can keep the recording and take it home if you like, I have nothing to fear because nobody is allowed to enter this room carrying any form of recording."

Inside the room is a PC with normal equippment, like loudspeakers, a sound card, windows operating system, all kinds of sound codecs, etc. But there is no recording of the key word on the computer or any other device or media in the room, and there is no way for the computer to communicate with anything outside the room, so no Internet, etc. Everything is like a lab used for the development of the technique of the security system of the vault and its automatic opening when the key word is uttered.

M now takes some money, locks the vault, and they both go out through a back door which is the normal exit from that room. One can only go out through the exit, not in.

A couple of days later, G comes to the vault room. The guards search him and find no recordings and thus let him in. Half an hour later G goes out the exit door with all the money from the vault.

How did he do it?

Solution