T H E H A C K E R ' S H A N D B O O K 

Copyright (c) Hugo Cornwall

All rights reserved

First published in Great Britain in 1985 by Century Communications Ltd

Portland House, 12-13 Greek Street, London W1V 5LE.

Reprinted 1985 (four times)

ISBN 0 7126 0650 5

Printed and bound in Great Britain by Billing & Sons Limited, Worcester.


Introduction vii

1 First Principles 5

2 Computer-to-computer communications 10

3 Hackers' Equipment 17

4 Targets: What you can find on mainframes 32

5 Hackers' Intelligence 44

6 Hackers' Techniques 66

7 Networks 77

8 Viewdata systems 94

9 Radio computer data 106

10 Hacking: the future 115


I troubleshooting 119

II Glossary 124

III CCITT and related standards 136

IV Standard computer alphabets 137

V Modems 144

VI Radio Spectrum 146
VII Port-finder flow chart 150


 The word 'hacker' is used in two different but associated

ways: for some, a hacker is merely a computer enthusiast of any kind,

who loves working with the beasties for their own sake, as opposed to

operating them in order to enrich a company or research project --or

to play games.

 This book uses the word in a more restricted sense: hacking is a

recreational and educational sport. It consists of attempting to make

unauthorised entry into computers and to explore what is there. The

sport's aims and purposes have been widely misunderstood; most

hackers are not interested in perpetrating massive frauds, modifying

their personal banking, taxation and employee records, or inducing

one world super-power into inadvertently commencing Armageddon in the

mistaken belief that another super-power is about to attack it. Every

hacker I have ever come across has been quite clear about where the

fun lies: it is in developing an understanding of a system and

finally producing the skills and tools to defeat it. In the vast

majority of cases, the process of 'getting in' is much more

satisfying than what is discovered in the protected computer files.

  In this respect, the hacker is the direct descendant of the phone

phreaks of fifteen years ago. Phone phreaking became interesting as

intra-nation and international subscriber trunk dialling was

introduced, but when the London-based phreak finally chained his way

through to Hawaii, he usually had no one there to speak to except the

local weather service or American Express office, to confirm that the

desired target had indeed been hit. One of the earliest of the

present generation of hackers, Susan Headley, only 17 when she began

her exploits in California in 1977, chose as her target the local

phone company and, with the information extracted from her hacks, ran

all over the telephone network. She 'retired' four years later, when

friends started developing schemes to shut down part of the phone


 There is also a strong affinity with program copy-protection

crunchers. Most commercial software for micros is sold in a form to

prevent obvious casual copying, say by loading a cassette, cartridge

or disk into memory and then executing a 'save' on to a

blank cassette or disk. Copy-protection devices vary greatly in

their methodology and sophistication and there are those who, without

any commercial motive, enjoy nothing so much as defeating them. Every

computer buff has met at least one cruncher with a vast store of

commercial programs, all of which have somehow had the protection

removed--and perhaps the main title subtly altered to show the

cruncher's technical skills--but which are then never actually used

at all.

 Perhaps I should tell you what you can reasonably expect from this

handbook. Hacking is an activity like few others: it is semi-legal,

seldom encouraged, and in its full extent so vast that no individual

or group, short of an organisation like GCHQ or NSA, could hope to

grasp a fraction of the possibilities. So this is not one of those

books with titles like Games Programming with the 6502 where, if the

book is any good and if you are any good, you will emerge with some

mastery of the subject-matter. The aim of this book is merely to give

you some grasp of methodology, help you develop the appropriate

attitudes and skills, provide essential background and some

referencing material--and point you in the right directions for more

knowledge. Up to a point, each chapter may be read by itself; I have

compiled extensive appendices, containing material which will be of

use long after the main body of the text has been absorbed.

 It is one of the characteristics of hacking anecdotes, like those

relating to espionage exploits, that almost no one closely involved

has much stake in the truth; victims want to describe damage as

minimal, and perpetrators like to paint themselves as heroes while

carefully disguising sources and methods. In addition, journalists

who cover such stories are not always sufficiently competent to write

accurately, or even to know when they are being hoodwink- ed. (A note

for journalists: any hacker who offers to break into a system on

demand is conning you--the most you can expect is a repeat

performance for your benefit of what a hacker has previously

succeeded in doing. Getting to the 'front page' of a service or

network need not imply that everything within that service can be

accessed. Being able to retrieve confidential information, perhaps

credit ratings, does not mean that the hacker would also be able to

alter that data. Remember the first rule of good reporting: be

sceptical.) So far as possible, I have tried to verify each story

that appears in these pages, but hackers work in isolated groups and

my sources on some of the important hacks of recent years are more

remote than I would have liked. In these

cases, my accounts are of events and methods which, in all the

circumstances, I believe are true. I welcome notes of correction.

 Experienced hackers may identify one or two curious gaps in the

range of coverage, or less than full explanations; you can chose any

combination of the following explanations without causing me any

worry: first, I may be ignorant and incompetent; second, much of the

fun of hacking is making your own discoveries and I wouldn't want to

spoil that; third, maybe there are a few areas which are really best

left alone.

 Nearly all of the material is applicable to readers in all

countries; however, the author is British and so are most of his


 The pleasures of hacking are possible at almost any level of

computer competence beyond rank beginner and with quite minimal

equipment. It is quite difficult to describe the joy of using the

world's cheapest micro, some clever firmware, a home-brew acoustic

coupler and find that, courtesy of a friendly remote PDP11/70, you

can be playing with Unix, the fashionable multitasking operating


 The assumptions I have made about you as a reader are that you own a

modest personal computer, a modem and some communications software

which you know, roughly, how to use. (If you are not confident yet,

practise logging on to a few hobbyist bulletin boards.) For more

advanced hacking, better equipment helps; but, just as very tasty

photographs can be taken with snap-shot cameras, the computer

equivalent of a Hasselblad with a trolley- load of accessories is not


 Since you may at this point be suspicious that I have vast

technical resources at my disposal, let me describe the kit that has

been used for most of my network adventures. At the centre is a

battered old Apple II+, its lid off most of the time to draw away the

heat from the many boards cramming the expansion slots. I use an

industry standard dot matrix printer, famous equally for the variety

of type founts possible, and for the paper-handling path, which

regularly skews off. I have two large boxes crammed full of software,

as I collect comms software in particular like a deranged

philatelist, but I use one package almost exclusively. As for

modems--well, at this point the set-up does become unconventional; by

the phone point are jack sockets for BT 95A, BT 96A, BT 600 and a

North American modular jack. I have two acoustic couplers, devices

for plunging telephone handsets into so that the computer can talk

down the line, at operating speeds of 300/300 and 75/1200. I also

have three heavy, mushroom coloured 'shoe-boxes', representing modem

technology of 4 or 5 years ago and operating at various speeds and

combinations of duplex/half- duplex. Whereas the acoustic coupler

connects my computer to the line by audio, the modem links up at the

electrical level and is more accurate and free from error. I have

access to other equipment in my work and through friends, but this is

what I use most of the time.

Behind me is my other important bit of kit: a filing cabinet.

Hacking is not an activity confined to sitting at keyboards and

watching screens. All good hackers retain formidable collections of

articles, promotional material and documentation; read on, and you

will see why.

 Finally, to those who would argue that a hacker's handbook must be

giving guidance to potential criminals, I have two things to say:

First, few people object to the sports of clay-pigeon shooting or

archery, although rifles, pistols and crossbows have no 'real'

purpose other than to kill things--and hackers have their own code of

responsibility, too. Second, real hacking is not as it is shown in

the movies and on tv, a situation which the publication of this book

may do something to correct. The sport of hacking itself may involve

breach of aspects of the law, notably theft of electricity, theft of

computer time and unlicensed usage of copyright material; every

hacker must decide individually each instance as it arises. Various people 

helped me on various aspects of this book; they must all remain unnamed--they 

know who they are and that they have my thanks.

First Principles

 The first hack I ever did was executed at an exhibition stand run

by BT's then rather new Prestel service. Earlier, in an adjacent

conference hall, an enthusiastic speaker had demonstrated view-

data's potential world-wide spread by logging on to Viditel, the

infant Dutch service. He had had, as so often happens in the these

circumstances, difficulty in logging on first time. He was using one

of those sets that displays auto-dialled telephone numbers; that was

how I found the number to call. By the time he had finished his third

unsuccessful log-on attempt I (and presumably several others) had all

the pass numbers. While the BT staff were busy with other visitors to

their stand, I picked out for myself a relatively neglected viewdata

set. I knew that it was possible to by-pass the auto-dialler with its

pre-programmed phone numbers in this particular model, simply by

picking up the the phone adjacent to it, dialling my preferred

number, waiting for the whistle, and then hitting the keyboard button

labelled 'viewdata'. I dialled Holland, performed my little by-pass

trick and watched Viditel write itself on the screen. The pass

numbers were accepted first time and, courtesy of...no, I'll spare

them embarrassment...I had only lack of fluency in Dutch to restrain

my explorations. Fortunately, the first BT executive to spot what I

had done was amused as well.

 Most hackers seem to have started in a similar way. Essentially

you rely on the foolishness and inadequate sense of security of

computer salesmen, operators, programmers and designers.

 In the introduction to this book I described hacking as a sport;

and like most sports, it is both relatively pointless and filled with

rules, written or otherwise, which have to be obeyed if there is to

be any meaningfulness to it. Just as rugby football is not only about

forcing a ball down one end of a field, so hacking is not just about

using any means to secure access to a computer.

 On this basis, opening private correspondence to secure a password

on a public access service like Prestel and then running around the

system building up someone's bill, is not what hackers call hacking.

The critical element must be the use of skill in some shape or form.

 Hacking is not a new pursuit. It started in the early 1960s when

the first "serious" time-share computers began to appear at

university sites. Very early on, 'unofficial' areas of the memory

started to appear, first as mere notice boards and scratch pads for

private programming experiments, then, as locations for games.

(Where, and how do you think the early Space Invaders, Lunar Landers

and Adventure Games were created?) Perhaps tech-hacking-- the

mischievous manipulation of technology--goes back even further. One

of the old favourites of US campus life was to rewire the control

panels of elevators (lifts) in high-rise buildings, so that a request

for the third floor resulted in the occupants being whizzed to the


 Towards the end of the 60s, when the first experimental networks

arrived on the scene (particularly when the legendary

ARPAnet--Advanced Research Projects Agency network-- opened up), the

computer hackers skipped out of their own local computers, along the

packet-switched high grade communications lines, and into the other

machines on the net. But all these hackers were privileged

individuals. They were at a university or research resource, and they

were able to borrow terminals to work with.

 What has changed now, of course, is the wide availability of home

computers and the modems to go with them, the growth of public-access

networking of computers, and the enormous quantity and variety of

computers that can be accessed.

 Hackers vary considerably in their native computer skills; a basic

knowledge of how data is held on computers and can be transferred

from one to another is essential. Determination, alertness,

opportunism, the ability to analyse and synthesise, the collection of

relevant helpful data and luck--the pre-requisites of any

intelligence officer--are all equally important. If you can write

quick effective programs in either a high level language or machine

code, well, it helps. A knowledge of on-line query procedures is

helpful, and the ability to work in one or more popular mainframe and

mini operating systems could put you in the big league.

 The materials and information you need to hack are all around

you--only they are seldom marked as such. Remember that a large

proportion of what is passed off as 'secret intelligence' is openly

available, if only you know where to look and how to appreciate what

you find. At one time or another, hacking will test everything you

know about computers and communications. You will discover your

abilities increase in fits and starts, and you must

be prepared for long periods when nothing new appears to happen.

 Popular films and tv series have built up a mythology of what

hackers can do and with what degree of ease. My personal delight in

such Dream Factory output is in compiling a list of all the mistakes

in each episode. Anyone who has ever tried to move a graphics game

from one micro to an almost-similar competitor will already know that

the chances of getting a home micro to display the North Atlantic

Strategic Situation as it would be viewed from the President's

Command Post would be slim even if appropriate telephone numbers and

passwords were available. Less immediately obvious is the fact that

most home micros talk to the outside world through limited but

convenient asynchronous protocols, effectively denying direct access

to the mainframe products of the world's undisputed leading computer

manufacturer, which favours synchronous protocols. And home micro

displays are memory-mapped, not vector-traced... Nevertheless, it is

astonishingly easy to get remarkable results. And thanks to the

protocol transformation facilities of PADs in PSS networks (of which

much more later), you can get into large IBM devices....

 The cheapest hacking kit I have ever used consisted of a ZX81, 16K

RAMpack, a clever firmware accessory and an acoustic coupler. Total

cost, just over ْ100. The ZX81's touch-membrane keyboard was one

liability; another was the uncertainty of the various connectors.

Much of the cleverness of the firmware was devoted to overcoming the

native drawbacks of the ZX81's inner configuration--the fact that it

didn't readily send and receive characters in the industry-standard

ASCII code, and that the output port was designed more for instant

access to the Z80's main logic rather than to use industry-standard

serial port protocols and to rectify the limited screen display.

 Yet this kit was capable of adjusting to most bulletin boards;

could get into most dial-up 300/300 asynchronous ports,

re-configuring for word-length and parity if needed; could have

accessed a PSS PAD and hence got into a huge range of computers not

normally available to micro-owners; and, with another modem, could

have got into viewdata services. You could print out pages on the ZX

'tin-foil' printer. The disadvantages of this kit were all in

convenience, not in facilities. Chapter 3 describes the sort of kit

most hackers use.

 It is even possible to hack with no equipment at all. All major

banks now have a network of 'hole in the wall' cash machines-- ATMs

or Automatic Telling Machines, as they are officially

known. Major building societies have their own network. These

machines have had faults in software design, and the hackers who

played around with them used no more equipment than their fingers and

brains. More about this later.

 Though I have no intention of writing at length about hacking

etiquette, it is worth one paragraph: lovers of fresh-air walks obey

the Country Code; they close gates behind them, and avoid damage to

crops and livestock. Something very similar ought to guide your

rambles into other people's computers: don't manipulate files unless

you are sure a back-up exists; don't crash operating systems; don't

lock legitimate users out from access; watch who you give information

to; if you really discover something confidential, keep it to

yourself. Hackers should not be interested in fraud. Finally, just

as any rambler who ventured past barbed wire and notices warning

about the Official Secrets Acts would deserve whatever happened

thereafter, there are a few hacking projects which should never be


 On the converse side, I and many hackers I know are convinced of one

thing: we receive more than a little help from the system managers of

the computers we attack. In the case of computers owned by

universities and polys, there is little doubt that a number of them

are viewed like academic libraries--strictly speaking they are for

the student population, but if an outsider seriously thirsty for

knowledge shows up, they aren't turned away. As for other computers,

a number of us are almost sure we have been used as a cheap means to

test a system's defences...someone releases a phone number and

low-level password to hackers (there are plenty of ways) and watches

what happens over the next few weeks while the computer files

themselves are empty of sensitive data. Then, when the results have

been noted, the phone numbers and passwords are changed, the security

improved etc etc....much easier on dp budgets than employing

programmers at £150/man/ day or more. Certainly the Pentagon has been

known to form 'Tiger Units' of US Army computer specialists to

pin-point weaknesses in systems security.

 Two spectacular hacks of recent years have captured the public

imagination: the first, the Great Prince Philip Prestel Hack, is

described in detail in chapter 8, which deals with viewdata. The

second was spectacular because it was carried out on live national

television. It occurred on October 2nd 1983 during a follow-up to the

BBC's successful Computer Literacy series. It's worth reporting here,

because it neatly illustrates the essence of hacking as a sport...

skill with systems, careful research, maximum impact with minimum real 

harm, and humour.

 The tv presenter, John Coll, was trying to show off the Telecom

Gold electronic mail service. Coll had hitherto never liked long

passwords and, in the context of the tight timing and pressures of

live tv, a two letter password seemed a good idea at the time. On

Telecom Gold, it is only the password that is truly confidential;

system and account numbers, as well as phone numbers to log on to the

system, are easily obtainable. The BBC's account number, extensively

publicised, was OWL001, the owl being the 'logo' for the tv series as

well as the BBC computer.

 The hacker, who appeared on a subsequent programme as a 'former

hacker' and who talked about his activities in general, but did not

openly acknowledge his responsibility for the BBC act, managed to

seize control of Coll's mailbox and superimpose a message of his own:

Computer Security Error. Illegal access. I hope your television

PROGRAMME runs as smoothly as my PROGRAM worked out your 


Nothing is secure!

Hackers' Song

"Put another password in,

Bomb it out and try again

Try to get past logging in,

We're hacking, hacking, hacking

Try his first wife's maiden name,

This is more than just a game,

It's real fun, but just the same,

It's hacking, hacking, hacking"

The Nutcracker (Hackers UK)



 After the hack a number of stories about how it had been carried

out, and by whom, circulated; it was suggested that the hackers had

crashed through to the operating system of the Prime computers upon

which the Dialcom electronic mail software

resided--it was also suggested that the BBC had arranged the whole

thing as a stunt, or alternatively, that some BBC employees had fixed

it up without telling their colleagues. Getting to the truth of a

legend in such cases is almost always impossible. No one involved has

a stake in the truth. British Telecom, with a strong commitment to

get Gold accepted in the business community, was anxious to suggest

that only the dirtiest of dirty tricks could remove the inherent

confidentiality of their electronic mail service. Naturally, the

British Broadcasting Corporation rejected any possibility that it

would connive in an irresponsible cheap stunt. But the hacker had no

great stake in the truth either--he had sources and contacts to

protect, and his image in the hacker community to bolster. Never

expect any hacking anecdote to be completely truthful.


Computer-to-Computer Communications

 Services intended for access by microcomputers are nowadays

usually presented in a very user-friendly fashion: pop in your

software disc or firmware, check the connections, dial the telephone

number, listen for the tone...and there you are. Hackers, interested

in venturing where they are not invited, enjoy no such luxury. They

may want to access older services which preceded the modern 'human

interface'; they are very likely to travel along paths intended, not for ordinary 

customers, but for engineers or salesmen; they could be utilising facilities that 

were part of a computer's commissioning process and have been hardly used 


 So the hacker needs a greater knowledge of datacomms technology than

does a more passive computer user, and some feeling for the history of the 

technology is pretty essential, because of its growth pattern and because of the 

fact that many interesting installations still use yesterday's solutions.
 Getting one computer to talk to another some distance away means

accepting a number of limiting factors:

( Although computers can send out several bits of information at

once, the ribbon cable necessary to do this is not economical at any

great length, particularly if the information is to be sent out over

a network--each wire in the ribbon would need switching separately,

thus making ex- changes prohibitively expensive. So bits must be

transmitted one at a time, or serially.

( Since you will be using, in the first instance, wires and networks

already installed--in the form of the telephone and telex

networks--you must accept that the limited bandwidth of these

facilities will restrict the rate at which data can be sent. The data

will pass through long lengths of wire, frequently being

re-amplified, and undergoing de- gradation as it passes through dirty

switches and relays in a multiplicity of exchanges.

( Data must be easily capable of accurate recovery at the far end.

( Sending and receiving computers must be synchronised in their working.

( The mode in which data is transmitted must be one understood by all 

computers; accepting a standard protocol may mean adopting the

speed and efficiency of the slowest.

( The present 'universal' standard for data transmission used by

microcomputers and many other services uses agreed tones to signify

binary 0 and binary 1, the ASCII character set (also known as

International Alphabet No 5), and an asynchronous protocol, whereby

the transmitting and receiving computers are locked in step every

time a character is sent, not just at the beginning of a transmission

stream. Like nearly all standards, it is highly arbitrary in its

decisions and derives its importance simply from the fact of being

generally accepted. Like many standards, too, there are a number of

subtle and important variations.

 To see how the standard works, how it came about and the reasons

for the variations, we need to look back a little into history.

The Growth of Telegraphy

 The essential techniques of sending data along wires has a history

of 150 years, and some of the common terminology of modern data

transmission goes right back to the first experiments.

 The earliest form of telegraphy, itself the earliest form of

electrical message sending, used the remote actuation of electrical

relays to leave marks on a strip of paper. The letters of the

alphabet were defined by the patterns of 'mark' and 'space'.
The terms have come through to the present, to signify binary

conditions of '1' and '0' respectively. The first reliable machine

for sending letters and figures by this method dates from 1840; the

direct successor of that machine, using remarkably unchanged

electromechanical technology and a 5-bit alphabetic code, is still

widely used today, as the telex/teleprinter/teletype. The mark and

space have been replaced by holes punched in paper-tape: larger holes

for mark, smaller ones for space. Synchronisation between sending and

receiving stations is carried out by beginning each letter with a

'start' bit (a space) and concluding it with a 'stop' bit (mark). The

'idle' state of a circuit is thus 'mark'. In effect, therefore, each

letter requires the transmission of 7 bits:

. * * . . . * (letter A: . = space; * = mark)

of which the first . is the start bit, the last * is the stop bit and

* * . .. is the code for A.

 This is the principle means for sending text messages around the

world, and the way in which news reports are distributed globally.

And, until third-world countries are rich enough to afford more

advanced devices, the technology will survive.
Early computer communications

 When, 110 years after the first such machines came on line, the

need arose to address computers remotely, telegraphy was the obvious

way to do so. No one expected computers in the early 1950s to give

instant results; jobs were assembled in batches, often fed in by

means of paper-tape (another borrowing from telex, still in use) and

then run. The instant calculation and collation of data was then

considered quite miraculous. So the first use of data communications

was almost exclusively to ensure that the machine was fed with

up-to-date information, not for the machine to send the results out

to those who might want it; they could wait for the 'print-out' in

due course, borne to them with considerable solemnity by the computer

experts. Typical communications speeds were 50 or 75 baud. (The baud

is the measure of speed of data transmission: specifically, it refers

to the number of signal level changes per second and is thus not the

same as bits-per-second.)

 These early computers were, of course, in today's jargon,

single-user/single-task; programs were fed by direct machine coding.

Gradually, over the next 15 years, computers spawned multi-user

capabilities by means of time-sharing techniques, and their human

interface became more 'user-friendly'.

 With these facilities grew the demand for remote access to

computers, and modern data communications began.

 Even at the very end of the 1960s when I had my own very first

encounter with a computer, the links with telegraphy were still

obvious. As a result of happenstance, I was in a Government-run

research facility to the south-west of London, and the program I was

to use was located on a computer just to the north of Central London;

I was sat down in front of a battered teletype--capitals and figures

only, and requiring not inconsiderable physical force from my

smallish fingers to actuate the keys of my choice. As it was a

teletype outputting on to a paper roll, mistakes could not as readily

be erased as on a VDU, and since the sole form of error reporting

consisted of a solitary ?, the episode was more frustrating than

thrilling. VDUs and good keyboards were then far too expensive for

'ordinary' use.

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