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Worms are nasty, but they certainly aren't new. Major portions of the early Internet were disabled by the Morris Worm way back in November 1988, but that wasn't even the first worm. In 1971, at Bolt Beranek and Newman (BBN), a researcher named Bob Thomas created a program that could move across a network of air traffic control systems, a startling target for such an early specimen. Thomas's so-called Creeper program moved from system to system, relocating its code between machines in an effort to help human air traffic controllers manage their work. Unlike worms, though, Creeper didn't install multiple instances of itself on several targets; it just moseyed around a network, attempting to remove itself from previous systems as it propagated forward.

Years later, the first true worm (i.e., self-replicating code that spread itself via a network) was devised by the brilliant folks at Xerox PARC. Yup, the same folks who created laser printers, the GUI, the mouse, and many other computer gadgets we use on a daily basis also created the first known true worm. However, they didn't plan on using worms as malicious tools. Two Xerox researchers named John F. Shoch and Jon A. Hupp just thought of worms as an amazingly efficient way to spread software to systems. Of course, they were right. Unfortunately, way back in the early 1980s, their first research worm accidentally escaped its captivity and started spreading throughout their own Xerox laboratory network, an ominous sign of worms to come. Today, attackers use the efficiency of worms to spread malware far and wide.

Worm releases really accelerated in the late 1990s and through this decade. The Melissa attack from March 1999 and the Love Bug attack of May 2000 caused many companies to disconnect from the Internet entirely for a day or two. Although most people refer to Melissa and the Love Bug as viruses, they actually were much more wormlike, spreading rampantly via the Internet. More recently, we've seen the Code Red and Nimda worms, which each compromised several hundred thousand machines in 2001. To this day, attackers around the globe are cooking up new and more devious worm recipes. These and other notable worm attacks are shown below. Take a careful look at this table to get a feel for how each of these major worm incidents impacted various systems.