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Undergound. Go to Table of Contents.

   sprinter, a simple computer program which automatically dialled a

   range of phone numbers looking for modems. If he turned the volume up

   on his modem when his computer dialled what seemed to be a dead or

   non-existent number, he sometimes heard a soft clicking noise after

   the disconnection message. The noise sounded like faint heartbeats.

  

   Curious, he experimented with these strange numbers and soon

   discovered they were disconnected lines which had not yet been

   reassigned. He wondered how he could use these odd numbers. After

   reading a document Mendax had found in Britain and uploaded to The

   Devil's Playground, another BBS, Trax had an idea. The posting

   provided information about CCITT #5 signalling tones, CCITT being the

   international standard--the language spoken by telephone exchanges

   between countries.

  

   When you make an international phone call from Australia to the US,

   the call passes from the local telephone exchange to an international

   gateway exchange within Australia. From there, it travels to an

   exchange in the US. The CCITT signalling tones were the special tones

   the two international gateway exchanges used to communicate with each

   other.

  

   Telecom Australia adapted a later version of this standard, called R2,

   for use on its own domestic exchanges. Telecom called this new

   standard MFC, or multi-frequency code. When, say, Trax rang Mendax,

   his exchange asked Mendax's to `talk' to Mendax's phone by using these

   tones. Mendax's exchange `answered', perhaps saying Mendax's phone was

   busy or disconnected. The Telecom-adapted tones--pairs of audio

   frequencies--did not exist in normal telephone keypads and you

   couldn't make them simply by punching keys on your household

   telephone.

  

   Trax wrote a program which allowed his Amstrad computer to generate the

   special tones and send them down the phone line. In an act many in the

   underground later considered to be a stroke of genius, he began to map

   out exactly what each tone did. It was a difficult task, since one tone

   could mean several different things at each stage of the `conversation'

   between two exchanges.

  

   Passionate about his new calling, Trax went trashing in Telecom

   garbage bins, where he found an MFC register list--an invaluable piece

   of his puzzle. Using the list, along with pieces of overseas phreaking

   files and a great deal of painstaking hands-on effort, Trax slowly

   learned the language of the Australian telephone exchanges. Then he

   taught the language to his computer.

  

   Trax tried calling one of the `heartbeat' phone numbers again. He

   began playing his special, computer-generated tones through an

   amplifier. In simple terms, he was able to fool other exchanges into

   thinking he was his local Telecom exchange. More accurately, Trax had

   made his exchange drop him into the outgoing signalling trunk that had

   been used to route to the disconnected phone number.

  

   Trax could now call out--anywhere--as if he was calling from a point

   halfway between his own phone and the disconnected number. If he

   called a modem at Melbourne University, for instance, and the line was

   being traced, his home phone number would not show up on the trace

   records. No-one would be charged for the call because Trax's calls

   were ghosts in the phone system.