Cryptic airwaves: number stations.....

Numbers stations (or number stations) are shortwave radio stations of uncertain origin. They 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, though sometimes male 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, but in 2001, the United States tried the Cuban Five for spying for Cuba. The group had received and decoded messages that had been broadcast from a Cuban numbers station.^[1] Also in 2001, Ana Belen Montes, a senior US Defense Intelligence Agency analyst, was arrested and charged with espionage. The federal prosecutors stated: "Montes communicated with the Cuban Intelligence Service through encrypted messages and received her instructions through encrypted shortwave transmissions from Cuba”. In 2006, Carlos Alvarez and his wife Elsa Alvarez were arrested and charged with espionage. The U.S. District Court Florida stated: "defendants would receive assignments via shortwave radio transmissions”. In June 2009, the United States similarly charged Walter Kendall Myers with conspiracy to spy for Cuba and receiving and decoding messages broadcast from a numbers station operated by the Cuban Intelligence Service to further that conspiracy.^{[2] [3]}
According to the notes of The Conet Project,^[4] numbers stations have been reported since World War I. If accurate, this would make numbers stations among the earliest radio broadcasts.
It has long been speculated, and was argued in court in one case, that these stations operate as a simple and foolproof method for government agencies to communicate with spies working undercover.^[5] According to this theory, the messages are encrypted with a one-time pad, to avoid any risk of decryption by the enemy. As evidence, numbers stations have changed details of their broadcasts or produced special, nonscheduled broadcasts coincident with extraordinary political events, such as the August Coup of 1991 in the Soviet Union.^[6]
Number Stations are also acknowledged for espionage purposes in Robert Wallace and H. Keith Melton's Spycraft (p. 438):^[7]

Others speculate that some of these stations may be related to illegal drug smuggling operations.^[8] Unlike government stations, smugglers' stations would need to be lower powered and irregularly operated, to avoid location by triangulated direction finding, followed by government raids. However, numbers stations have transmitted with impunity for decades, so they are generally presumed to be operated or sponsored only by governments. Also, numbers station transmissions in the international shortwave bands typically require high levels of electric power that is unavailable to ranches, farms, or plantations in isolated drug-growing regions.