Tracking the Lincolnshire Poacher 

A quick link to a recent Radio 4 programme -
Tracking the Lincolnshire Poacher (RealAudio; programme starts two minutes in) - about clandestine shortwave number stations, broadcasting streams of digits on behalf of the intelligence agencies. There's an interesting diversion into the theory and practice of covert channels and one-time pads (featuring an interview with
Bruce Schneier), and I'm delighted to find that the
Conet Project (from whom I pilfered the image above) is actually selling a CD boxed set of recordings. I
so want a copy.
(Update: it appears that Radio 4 have recycled the above URL, even though it explicitly names the programme, but there's a Windows Media Player version at
http://www.swldxer.co.uk/bbcr4.wma.)