"Numbers stations (or number stations) are shortwave radio stations of uncertain origin. In the 1950s, Time magazine reported that the numbers stations first appeared shortly after the war (World War II) and were using a format that had been used to send weather data during that war.
Numbers stations generally broadcast artificially generated voices reading streams of numbers, words, letters (sometimes using a spelling alphabet), tunes or Morse code. They are in a wide variety of languages and the voices are usually female, although sometimes men's or children's voices are used.
Evidence supports popular assumptions that the broadcasts are used to send messages to spies. This usage has not been publicly acknowledged by any government that may operate a numbers station, although two QSLs have been received from numbers stations by shortwave listeners who sent reception reports to said stations, which is the expected behaviour of a non-clandestine station."
An artificially generated child's voice reading random strings of numbers to spies?! NOPE, not creepy at all..
Now, to be fair, this really isn't as strange until you actually hear one. So, check out this video. And this one too.
I've actually been able to pick up one of the Cuban ones on a small shortwave that I own. At 3 am that shit is very unsettling.