Spying By Numbers

Ever since I read in William Poundstone's Big Secrets about the mysterious so-called "numbers stations" found on the shortwave radio band, I've found them oddly fascinating.

For those who don't know what a numbers station is, Salon ran a fairly informative article on them several years ago. Here's a bit from the article:

Twisting the dial of your shortwave radio, you come across the most "experimental" sounding station you've ever heard. A glockenspiel tune is followed by the voice of a little girl speaking numbers and letters in what sounds like a random order. A techno DJ's pirate radio remix? Performance art? No, you've stumbled across a "numbers station," and the message inside the madness just wasn't meant for you. Somewhere in the world, a government spook, maybe CIA, MI6 or Mossad, is furiously scrawling down the numbers on a pad, a decoding key open at his side.

More details, links and audio clips (which I find unnervingly creepy for some reason) can be found here and here, for starters.