Sasser: The worst computer worm in all of computer virus history. It shut off air control towers and infected millions of computers all around the world.
XP: The most common operating system right now. Before, this title was held by MS-DOS. The history is below:
Windows 1.0 def. MS-DOS
Windows 2.0 def. Windows 1.0
Windows 3.1 def. Windows 2.0
Windows 3.11 def. Windows 3.1
Windows NT def. Windows 3.1 and Windows 3.11
Windows XP def. Windows 1.0, Windows 2.0, MS-DOS, Windows 3.1, Windows 3.11, and Windows NT