This set is a collection of recordings of shortwave radio broadcasts; encrypted, presumably, in the service of espionage.
The majority of the 152 recordings included here are of voices (usually sampled or computerized) reading lists of numbers or phonetic letters in numerous languages; the broadcasts are made by what are commonly referred to as "numbers stations."
The thick booklet that is included (so large it comes in its own jewel case) documents the various stations and broadcasts -- read that for in-depth info.
The Conet Project was originally released in 1997 and quickly sold out. After a seemingly interminable period of unavailability, Irdial saw fit to re-release it in 2000.
On initial listen, the material is oddly compelling. After reading the booklet, it becomes a fascinating glimpse into a world that our real-life knowledge of is limited, if not non-existant. Material from this collection has appeared on albums (woven into songs) by artists such as Stereolab. "Pause" on their album Transient Random-Noise Bursts... features part of The Swedish Rhapsody (disc 1, track 1 of the Conet Project) throughout.
J Church (on "Stars Are Exploding" from their 2000 album One Mississippi), and Cinerama (on their second full-length album, if memory serves) have included segments of these recordings as well.
For even more information, check Simon Mason's site. He wrote the book on numbers stations -- literally. While his 1991 book, Secret Signals, is currently out of print, it's available for free online, along with dozens of links to articles and even sound files.