For Prime Suspect and Mendax, who were increasingly paranoid about line traces from the university modems they used as launchpads, Trax's phreaking skills were a gift from heaven.
Trax made his great discovery by accident. He was using a phone 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.
Trax continued to refine his ability to manipulate both the telephone and the exchange. He took his own telephone apart, piece by piece, countless times, fiddling with the parts until he understood exactly how it worked. Within months, he was able to do far more than just make free phone calls. He could, for instance, make a line trace think that he had come from a specific telephone number.