Challenge 2
                             By
                         Horny Toad


The challenge for this time is to customize and personalize
the code in tutorial 2.  In the directory Cdbkutl included
with this zine, you will find the file Toad2.asm.  This file
contains the listing for the COM Appending virus in the
tutorial.  What you need to do is modify it and make it your
own.  There are plenty of things that you can do to the code
to personalize it.  Use the code as a skeleton and build
upon it. Below, I will list a number of things that you can
do with the code.  I am purposely not going to guide you
through each step.  I want you to try them yourself and be
creative.  The only way you are going to learn how to code
virii is to actually do it yourself.

1. What are the other ways that you could check if a file
has already been infected?
 You could put an ID byte within the code that the virus
could check for. For example, after the jump is written to
the beginning of the file, an ID byte could also be written.
db 0e9h,0,0   ;the jump to the main virus body
db `T'            ;ID byte - T for Toad
You would then have to read and compare (cmp) the fourth
byte with `T' to see if the file has been previously
infected.

2. Start thinking about anti-anti-virus techniques.  When
you go in and change aspects of the file, the date and time
on the file changes to reflect this.  How could you save the
date and time of the file once you opened it, then restore
them right before closing?
Int 21 AX=5700 - Get file's date and time
Int 21 AX=5701 - Set file's date and time
Set file handle in BX. (Hint: If done write after the
int21/AH=3dh, file handle will be in AX)
The returned values in CX will be the time and DX will hold
the date.
(Hint: Store them in the data area and restore them just
before close)
mov word ptr [bp+time],cx  ;example of saving file time with
                           ;5700
mov cx,word ptr [bp+time]  ;example of restoring file time
                           ;with 5701

3. Include a signature in the code to personalize it.
For example:
credits db  `Toad2 written by Horny Toad',0
Or something that leaves your mark.

Just try to play around with it.  Giving you specific ways
to customize a virus doesn't make it unique.  Use your
imagination.  Make mistakes, at this level of virus writing,
mistakes are usually very easy to correct.

Good luck!