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Ben de Jong Discusses Secret Messages Send by Number Stations on Dutch NPO Radio 1

Ben de Jong, a guest lecturer at the Institute of Security and Global Affairs, appeared as a guest on NPO Radio 1 to discuss number stations that are used to send secret messages to spies in enemy territories.

A number station is a shortwave radio station that is used by spies. The station sends out coded messages. It is an old technique that is still being used today. 'It was deployed when a human source was operating on enemy territory,' explains de Jong. 'This source knew he had to listen to the station at a specific time. Each spy had his own code and a code book at home to translate the series of numbers to words.'

De Jong explains that it was useful method to send messages from headquarters back home to the spy without others being able to trace the spy. 'It's one-way traffic. The senders can be traced but that's absolutely useless without the code book.' So how do you catch someone? De Jong explains that in case of a suspect, that person could be put under surveillance to find out if they were listening to a number station and at which times. 'This way you're at least able to see if there's a connection.'

Secret messages in Youtube films

It may sound like something out of a Cold War film but in reality the stations still exist today. ‘New ways have been developed to communicate messages and to hide codes in, for instance, films posted Youtube, says De Jong. These are usually ordinary films that can get lost easily in all the other films that are posted on the platform, but these contain a hidden message. 'A normal person looking at them wouldn't even notice it, only if you know the code will you be able to see it'. An advantage is that this works both ways unlike the number stations. Those are strictly one-way traffic. 

You can listen to the full segment (in Dutch) here.

Dr. Ben de Jong is a guest researcher in the field of intelligence services at the Institute of Security and Global Affairs of Leiden University. He was previously a guest researcher at the University of Amsterdam.

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