Background & History
Origins
The requirement for sophisticated call-logging equipment goes back to 1984, when the Network, Systems and Technical Security Group of British Telecom's Network Operational Support unit (NOS) was investigating the irregular activities of certain computer hackers.
The case in question involved the hacking of the Duke of Edinburgh's Prestel account by Steve Gold and Robert Schifreen — a landmark case that ultimately led to the creation of the Computer Misuse Act 1990. At the time, no equipment existed to provide reliable evidence of fraudulent computer access. A prototype device — the data monitor — was rapidly developed and assembled to meet this need.
When the case came to trial, timing discrepancies of up to three minutes between the data monitor, its associated call logger, and the hacked computer system became a significant feature of the proceedings. To prevent such problems in future investigations, the data monitor was expanded to include its own integrated call-logging capability.
The standalone call-logging element was subsequently developed independently as the Line Event Recorder (LER) — accurate, reliable and highly portable. A further development, sponsored by NOS, added metering detection and a complete redesign of the hardware, producing the Monolog system described here.
↗ BBC News — Archive of historic BT email hack preserved
Postscript
Where does Monolog fit in the 21st Century?
Probably nowhere — and that is not entirely a sad thing. The introduction of per-second call pricing in 1998, followed by the phased withdrawal of the Meter Pulse Facility (MPF) between March 2007 and September 2008, effectively removed most of Monolog's core purpose. Without MPF, the ability to independently verify a subscriber's billing — the very reason Monolog existed — was largely lost.
The original support software — DIALOG, CHECKLOG, PRINTOUT — was written for 16-bit and 32-bit MS-DOS environments. In today's 64-bit world, none of it runs natively without an emulator, and its command-line character sits awkwardly alongside modern graphical interfaces. The underlying hardware faces a more fundamental problem still: it is built entirely around low-speed analogue dial-up technology, which is now largely obsolete.
The gradual demise of the traditional analogue telephone line — and the UK PSTN closure scheduled for January 2027 — marks the final chapter. Monolog is a product of its era: ingeniously conceived, carefully engineered, and now a piece of telecommunications history.
