In a recent article, I discuss the problems that arise from zombies and botnets. A zombie being a computer that has been comprimised by a malicious hacker to preform malicious actions against other computers. A collection of these zombies are referred to as botnets.
The link here is fromteh Washington Post and provides a great graphical step-by-step on how these botnets are created. Is it a tutorial on comprimising network computers? Not at all. What it does provide is a reference on how one mistake could wind up comprimising a network of computers.
http://www.washingtonpost.com/wp-dyn/content/custom/2006/02/17/CU2006021701353.html