PBS.org has a great cameo piece on a recent Bot Net attack on Estonia. That's right, a coordinated attack on pretty much the whole country. Watch the video if you're curious what a Bot Net is or want to understand the power/vulnerability of the Internet.
For the full-size version, go here: http://www.pbs.org/kcet/wiredscience/video/83-world_war_2_0.html.