Dirk Rijmenants has published a 10 page paper:
Cuban Agent Communications, Failure of a Perfect System.
Several Cuban spies in the United States, who received instruction from Cuba via shortwave numbers stations, were recently arrested. How did they fail?
Download link on his blog, also can be downloaded on his website, which is linked to, Dirk Rijmenants’ Cipher Machines and Cryptology,
Historical and Technical Information about Crypto Machines, Cryptology and Free Software Simulations.
Blog entry:
http://rijmenants.blogspot.com/2010/02/cuban-agent-communications.html
Info via dxld