The Slammer worm (also known as the Sapphire worm) was the fastest worm in history -- it doubled in size every 8.5 seconds at its peak. From the time it began to infect hosts (around 05:30 UTC) on Saturday, Jan. 25, 2003 it managed to infect more than 90 percent of the vulnerable hosts within 10 minutes using a well known vulnerability in Microsoft's SQL Server. Slammer eventually infected more than 75,000 hosts, flooded networks all over the world, caused disruptions to financial institutions, ATMs, and even an election in Canada. Here's a map that shows how quickly the worm spread over the first half-hour of tracking (Macromedia Flash required).