How to write a computer virus

Introduction ..................................... 5



PART 1. COM - VIRUSES ....................... 6


CHAPTER 1. DEVELOPMENT OF NON-RESIDENT

Virus programs .............. 6

1.1 Download and run

COM - Programme ..................... 6

1.2 How the virus can infect

COM - file .......................... 7

1.3 Operation of the virus in

infected program ................ 8

1.4 How to start

spread of the virus .............. 9

1.5 Getting Started ....................... 10

1.6 The virus gets control ........... 10

1.7 Restoring infected

program ........................... 12

1.8 Remember the contents of DTA ........... 12

1.9 We are looking for a suitable file ................ 13

1.10 Read the original three bytes ........... 15

1.11 We perform the necessary calculations ....... 16

1.12 checks the file for infection ...... 18

1.13 infect COM - program ............ 19

1.14 Restoring the DTA ................. 20

1.15 passes control

infected program ................ 20

1.16 The data area virus program ... 21

1.17 Completing the run programs ..... 21

1.18 The text of non-resident COM - virus ... 23

1.19 Comments ......................... 29

1.20 Test virus .................... 29


CHAPTER 2. DEVELOPMENT resident

Virus programs .............. 30

2.1 The concept of resident

(TSR) virus ...................... 30

2.2 A few words about

resident programs .............. 30

2.3 The algorithm works

resident COM - virus ........... 31

2.4 Title virus .................... 34

Virus 2.5 starts ............... 34

2.6 Save CPU registers ....... 38

2.7 Create section

initialization ....................... 39

2.8 requests a block of memory ............. 41

2.9 Making virus "invisible" ......... 44

2.10 Get interrupt vector ......... 46

2.11 Copy the virus code in memory ...... 48

2.12 Set the interrupt vector

viral handlers ............. 48

2.13 Writing resident portion ............. 50

2.14 infect COM - file ................. 51

2.15 Restoring registers ............ 56

2.16 Writing hooks ........ 57

2.17 handler Int 13h .................. 58

2.18 handler Int 21h .................. 60

2.19 handler Int 24h .................. 62

2.20 Handler Int 2Fh .................. 62

2.21 handler Int 28h .................. 64

2.22 The data area virus ............... 64

2.23 The identification procedure COMMAND.COM .. 65

2.24 completes the program ................. 66

2.25 Text resident COM - virus ..... 67

2.26 Comments ......................... 81

2.27 Test virus .................... 82



PART 2. EXE - VIRUSES ....................... 82


CHAPTER 1. DEVELOPMENT nonresident

EXE - VIRUS .................... 82

1.1 Format EXE - file on disk ......... 82

1.2 Download and run

EXE - programs ..................... 84

1.3 How the virus can infect

EXE - File .......................... 86

1.4 Operation of the virus in

infected program ................ 86

1.5 Getting Started ....................... 88

1.6 The virus gets control ........... 88

1.7 We are looking for a suitable file ................ 89

1.8 Reading the header file .............. 92

1.9 manufacture optionally