Propagation
On March 19, 2004, the 'Witty' worm began infecting hosts connected to the Internet (and running the vulnerable ISS software) from a "seed" population, probably of previously compromised computers. Within a half-hour it infected 12,000 computers and was generating 90 Gbit/s (gigabits per second) of UDP traffic.
Read more about this topic: Witty (computer Worm)