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To prevent pirates from making unauthorised copies of songs, some CDs just will not play on a PC. Now, First 4 Internet of Banbury, near Oxford, UK, has patented a technique which it believes will allow CDs to be played but not copied on a PC (GB 2 386 245). The trick is to place two versions of the music on the CD. One plays on an ordinary CD player but not on a PC. The other version will play on a PC but only after the user downloads some software from the disc. This decodes the music and senses any attempt to copy the disc, in which case it shuts down.