Y L F M A E T Team-Fly® Blind Folio i Viruses Revealed David Harley, Robert Slade, Urs Gattiker Osborne/McGraw-Hill New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto Copyright © 2001 by The McGraw-Hill Companies, Inc. All rights reserved. Manufactured in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data- base or retrieval system, without the prior written permission of the publisher. 0-07-222818-0 The material in this eBook also appears in the print version of this title: 0-07-213090-3. All trademarks are trademarks of their respective owners. Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the benefit of the trademark owner, with no intention of infringement of the trademark. 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Your right to use the work may be terminated if you fail to comply with these terms. THE WORK IS PROVIDED “AS IS”. McGRAW-HILL AND ITS LICENSORS MAKE NO GUAR- ANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMA- TION THAT CAN BE ACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. McGraw-Hill and its licensors do not warrant or guarantee that the func- tions contained in the work will meet your requirements or that its operation will be uninterrupted or error free. Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inac- curacy, error or omission, regardless of cause, in the work or for any damages resulting therefrom. McGraw-Hill has no responsibility for the content of any information accessed through the work. Under no circumstances shall McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages. This limitation of lia- bility shall apply to any claim or cause whatsoever whether such claim or cause arises in contract, tort or otherwise. DOI: 10.1036/0072228180 Blind Folio iii It has been said, in regard to computer network communities, that no community is worthy of the name until it has had a wedding and a funeral. We, in the computer virus research tribe, have had both. We will not embarrass the newlyweds here. We wish, however, to dedicate this book to the memory of Ysrael Radai and Harold Joseph Highland. Their contributions to our field, and to so many others, are appreciated, and they will be sorely missed. To the Meeter Machine, and its viral output. —Robert Slade To my daughter Katie, my constant reminder that computer security should not be confused with real life. Now, perhaps, we’ll have time to play Monopoly. Also to my mother, Gwendoline Harley, for being an honorary parent to Katie when I had to find time for Baby Book. —David Harley Dedicated to my friends Inger Marie, Melanie, Lars, Rainer, Stefano, and all my current and past students who continue in keeping me going when obstacles seem insurmountable. —Urs Gattiker This page intentionally left blank. For more information about this title, click here. Table of Contents Foreword . xxi About the Authors . xxv Acknowledgments . xxix Introduction . xxxi I The Problem 1 Baseline Definitions . 3 Computer Virus Fact and Fantasy . 4 Definitions . 5 Viruses and Virus Mechanisms . 6 Virus Structure . 7 Damage . 7 Damage Versus Infection . 8 Stealth Mechanisms . 9 Polymorphism . 10 What Is This, a UNIX Textbook? . 10 Diet of Worms . 12 Trojan Horses . 12 In the Wild . 13 Instant Guide to Anti-Virus Software . 15 Summary . .16 2 Historical Overview . 17 Virus Prehistory: Jurassic Park to Xerox PARC . 18 Wormholes . 19 Core Wars . 19 The Xerox Worm (Shoch/Hupp Segmented Worm) . 20 Real Viruses: Early Days . 22 v Copyright 2001 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use. vi Viruses Revealed 1981: Early Apple II Viruses . 22 1983: Elk Cloner . 23 1986: © BRAIN . 25 1987: Goodnight Vienna, Hello Lehigh . 26 1988: The Worm Turns . 27 The Internet Age . .30 1989: Worms, Dark Avenger, and AIDS . 30 1990: Polymorphs and Multipartites . 32 1991: Renaissance Virus, Tequila Sunrise . 33 1992: Revenge of the Turtle . 34 1993: Polymorphism Rules . 36 1994: Smoke Me a Kipper . 37 1995: Microsoft Office Macro Viruses . 38 1996: Macs, Macros, the Universe, and Everything . 39 1997: Hoaxes and Chain Letters . 40 1998: It’s No Joke . 40 1999: Here Comes Your 19th Server Meltdown . 41 2000: Year of the VBScript Virus/Worm . 43 And So It Goes... 48 Summary . .49 3 Malware Defined . 51 What Computers Do . 52 Virus Functionality . .53 Application Functionality Versus Security . 53 In-the-Wild Versus Absolute Big Numbers . 54 What Do Anti-Virus Programs Actually Detect? . 57 Viruses . 58 Worms . 61 Intendeds . 62 Corruptions . 63 Germs . 64 Droppers . 64 Test Viruses . 65 Generators . 65 Trojans . 66 Password Stealers and Backdoors . 70 Jokes . 71 Contents vii Remote-Access Tools (RATs) . 74 DDoS Agents . 75 Rootkits . 77 False Alarms . 77 Summary . .79 4 Virus Activity and Operation . 81 How Do You Write a Virus? . 83 Tripartite Structure . 87 Infection Mechanism . 87 Trigger . 88 Payload . 88 Replication . 90 Non-Resident Viruses . 91 Memory-Resident Viruses . 91 Hybrid Viruses . 92 Generality, Extent, Persistence . ..