To make your victim think that they have a virus...
First, score some time on their computer. Before doing these pranks, set it so that you can see file extensions, (check "Show extensions for known file types in folder options,)and set it so you can see all types of files (Folder options: Check "Show all files") Next, do any and/or all of these things...
#1: Loading Screen
Find the file named logo.sys on drive C. Rename it to logo.bmp and Modify the image to something funny. After modifying, save, and rename it back to logo.sys
#2: Loading messages
Press start, run, and type in (without the quotes,) "msconfig"
Next, choose the tab called autoexec.bat and... First, you click new, and in the little text box, type "@echo off" (without the quotes) If @echo off isn't right at the top of the list in autoexec.bat, select it and use the move up and move down buttons to get it to the top. Next, make another line called "cls" (no quotes) and move it just under @echo off . Now the fun begins! Add lines anywhere below @echo off and cls following this format (minus the quotes...) "echo Your message here" Make as many of them as you want. It is funny!
#3 Desktop settings.
Just right click on the desktop and choose "Display properties" and wreak havoc on the settings! I like to change the icon spacing, color schemes, and... yeh. I also make "You have a virus!" Wallpapers and I put 'em up on the desktop.
#4 Prank software!
Load prank software into your victims startup folder! It is funny AS!
Well, that's all, and... don't blame me when the victim is after your blood! ;-)