right, firstly right click on your desktop and select new shortcut.
right click>new>shortcut
now when it asks for the address of the shortcut type:
shutdown -c -s -t 50 -c "Write what message you want to appear here"
save and voila... your fake virus!

to change what the icon looks like do this:
right click on icon>shortcut>change icon

I personally make it look like IE and name it that aswell.
Have fun spreading!