Computer viruses - a high-tech disease.pdf

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COmPUT6R
o high-tech dLrea-ne
Ralf Buiger
Abacus!!
A Data Becker Book
lia
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Second Edition, December 1988
Printed in U.S.A.
Copyright © 1987,1988
Data Becker, GmbH
Merowingerstrafie 30
4000 Dusseldorf, West Germany
Copyright © 1988
Abacus
5370 52nd Street, SE
Grand Rapids, MI 49508
This book is copyrighted. No part of this book may be reproduced, stored in a retrieval
system, or transmitted in any form or by any means, electronic, mechanical, photocopying,
recording or otherwise without the prior written permission of Abacus Software or Data
Becker, GmbH.
Every effort has been made to ensure complete and accurate information concerning the
material presented in this book. However, Abacus Software can neither guarantee nor be
held legally responsible for any mistakes in printing or faulty instructions contained in this
bode. The authors always appreciate receiving notice of any errors or misprints.
The programs presented in this book are for demonstration and testing purposes only.
Abacus Software will take no responsibility new can be held legally responsible for damages
caused by improper handling or use of the demonstration programs.
Amiga 500, Amiga 1000 and Amiga 2000, are trademarks or registered trademarks of
Commodore-Amiga Inc.
IBM, AT, XT and PC are trademarks or registered trademarks of International Business
Machines, Inc.
MS-DOS and Microsoft Word are trademarks or registered trademarks of Microsoft
Corporation.
WordStar is a registered trademark of MicroPro International.
Tuibo Pascal is a registered trademark of Borland International.
Atari ST, ST and Atari are trademarks or registered trademarks of Atari Corporation.
ISBN
1-55755-043-3
ii
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Table of Contents
Part 1 The background of computer viruses
1
1.
What are computer viruses?
3
1.1
Data processing terms
7
1.2
Program Modification
9
1.3
Data Modification
10
1.4
Properties of virus programs
13
1.5
Definition of a virus program
15
2.
Historical review
17
2.1
Glasnost? The studies of Fred Cohen
20
3.
Dangers from computer viruses
27
3.1
The legend of positive viruses
32
3.2
Virtually impossible to trace
34
3.3
From software to soft war
35
4.
Status quo of virus research
37
4.1
Chaos Communication Congress, Dec. 1986
40
4.2
Secret studies?
42
5.
Live with the danger?
45
5.1
Comments about viruses
48
5.2
Ignorance is bliss
53
5.3
An informative discussion
55
6.
Examples of viruses
59
6.1
Diagnosis: Virus attack?
62
6.2
Crasher viruses
66
6.3
Can viruses destroy hardware?
68
6.4
Error simulation viruses
69
6.5
Target: Data
70
6.6
Theft of computer time
71
6.7
Taking advantage
72
6.8
Extortion
73
6.9
Industrial and other espionage
74
6.10 Pros and cons of passwords
75
6.11 Theft protection virus
77
7.
Protection strategies
79
7.1
Software
82
7.2
Data
84
7.3
The system
86
7.4
The users
87
7.5
Computer misuse insurance
88
Part 2 Computer viruses in practice
9 3
8.
Real computer viruses
95
8.1
Overwriting viruses
98
8.2
Non-overwriting viruses
100
8.3
Memory-resident viruses
104
iii
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COMPUTER VIRUSES: A HIGH-TECH DISEASE
TABLE OF CONTENTS
8.4
Calling viruses
107
8.5
Other viruses
109
8.6
Demonstration software
110
8.7
VIRDEM.COM
121
9
Languages for virus programming
125
9.1
Viruses in assembly language
128
9.2
Viruses in Pascal
159
9.3
Viruses in BASIC
163
9.4
Batch viruses
166
9.5
Infections in the source code
173
10.
Various operating systems
177
10.1 MS-DOS
180
10.2 Viruses under CP/M
184
10.3 Networks
186
11.
Paths of infection
191
11.1 Viruses in the carrier program
194
11.2 Viruses by phone
198
11.3 Paths through the isolation
199
11.4 Programmers
202
12.
The security
risks
203
12.1 Data protection and service
208
12.2 VIR-DOS?
210
12.3 Randomly occurring viruses
211
13.
Manipulation tasks
217
13.1 Nothing's as easy as a crash
220
13.2 Software vs. hardware
223
13.3 False errors
225
13.4 Data manipulations
227
13.5 This far and no farther
228
14.
Protection strategies
229
14.1 Virus-proof operating systems
232
14.2 Protection through self-mutilation
233
14.3 Virus hunter programs
234
14.4 Protection viruses
242
14.5 Hardware protection
243
14.6 Alteration searcher
248
14.7 What do you do when you're infected?
253
14.8 Away with the standard?
255
15.
A look at the future
259
15.1 What will the software of the future look like?
262
15.2 EDP high-security complex
264
15.3 Are viruses controllable?
267
15.4 A way to artificial intelligence?
269
Index
275
iv
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Preface
The topic of this book has recently reared its (ugly) head. Several com-
merical and government computer systems were stricken with computer
virus epidemics, effectively shutting down the computer networks and
interrupting the work of hundreds of users.
Since Abacus also publishes computer software, we are acutely aware of
the offensive nature of computer viruses. Their potential for destruction
should not be underestimated.
Our purpose in publishing this book is to shed as much light on
computer viruses as possible. Our goal is to make all users aware of the
problems that can arise from casually sharing programs - whether they
come from diskettes or over networks.
Some readers may feel that the virus examples in the book should be
omitted. It should be made clear that we have printed the examples to
illustrate how easy it is to write a virus. Surely anyone who is bent on
destruction will have the know-how to create far more sophisticated and
•harmful viruses. On the other hand, unless you know how a virus oper-
ates, it is difficult to protect against them.
We encourage your feedback about this book and your experiences with
and protecting against computer viruses.
ArnieLee
November 1988
v
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