An electronic magazine, The International Subversive had a simple editorial policy. You could only have a copy of the magazine if you wrote an `article'. The policy was a good way of protecting against nappies--sloppy or inexperienced hackers who might accidentally draw police attention. Nappies also tended to abuse good phreaking and hacking techniques, which might cause Telecom to close up security holes. The result was that IS had a circulation of just three people. To a non-hacker, IS looked like gobbledygook--the phone book made more interesting reading. But to a member of the computer underground, IS was a treasure map. A good hacker could follow the trail of modem phone numbers and passwords, then use the directions in IS to disappear through secret entrances into the labyrinth of forbidden computer networks. Armed with the magazine, he could slither out of tight spots, outwit system admins and find the treasure secreted in each computer system. 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.