I have spoken of Numbers stations in the past, however I wanted to take the time to go into them a little more in depth. Firstly, for those that don't know, numbers stations are base stations which traditionally operate Shortwave transmitters, and broadcast a series of letters, numbers, or short data bursts. These stations often vary their frequency and the time at which they send their messages. To this day, it is still the most secure way to send spies in the field, encrypted messages or instructions.
I guess the first questions people would ask are "How do we know these are used for spying?". We know that as far back as World War II a version of numbers stations were used to aide the French Resistance. Since then every major government in the world has had a Numbers station originating from land under their control. The Linconshire Poacher, likely the most famous of them all, originates from Cyprus, and is operated by MI6.
The Conet Project contains hundreds of recordings of Numbers Stations and other strange broadcasts. Be sure to check it out!
The system works because the sender sends out a code of various letters or numbers. Often these would be arranged in groups of 4 or 5 characters. Messages often start with 'Group' designations which act as the 'to' header in a message. Then a message is sent as such; Alpha, Lima, Bravo, Delta, Lima... Juliet, Oscar, Mike, Quebec, Bravo... Hotel, Kilo, Foxtrot, Oscar, Oscar... Mike, Lima, Tango, Golf, Bravo...
The operative, then decodes the message by comparing the message to a one time pad, which is a dated key which will only work on the date or message that it is intended for, and then must be destroyed. The pad allows the radio message to be decoded by adding values of the message and the key, then applying a randomizer with a final decrypted message being tallied up from the total plus the randomizer. This can also be done with numbers as well.
Numbers stations are still active, and in some ways more active then ever before. Many have moved to using RTTY or other semi-digital methods to transmit bursts of encrypted messages. Recently during a camp fire discussion, I found out from someone that apparently there are numbers stations on the telephone now. 1-800 numbers are being found which auto answer and blurt out a series of numbers, then hang up. One such number being 1-800-469-6002. I am unsure the purpose of this number, but it apparently tracks back to a political office in El Paso, TX. I imagine it is involved in intelligence of some sort. I found it funny that some random poster appeared on a discussion board which relates to 1-800 numbers, and told people not to worry about this number and to delete it and not comment about it. That alone makes it suspicious.
I don't know if 1-800 numbers are quite as secure as shortwave radio broadcasts however. Foreign governments could always place flags on 1-800 calls on their telecommunication systems and auto record them to find out if number stations are being called and where they originate from. Obviously a smart spy would go to a pay phone, but it wouldn't be too hard to track down. Also, I am unsure? Do 1-800 numbers work over seas as well? Or is this only a North America service? If it is only North America, what is the purpose of a numbers station on our own soil?
Ah it is fun to wonder about the unknown. I am sure the government hates having smart people figure out what their doing, but I suppose that is why Obama wants to ban Conspiracy Theorists.