US probing Monday's attack on the Internet
More details, including the news that the FBI is investigating the attack, according to this AP story printed in this Wall Street Journal story (subscription required):
One person familiar with the Monday attack described it as the most sophisticated and large-scale assault against these crucial computers in the history of the Internet. The origin of the attack was unknown; the Federal Bureau of Investigations and White House said they were investigating the incident.
Seven of the 13 servers failed to respond to legitimate network traffic and two others failed intermittently during the attack, officials said.
...Monday's attack wasn't more disruptive because many Internet providers and large corporations and organizations routinely store, or "cache," popular Web directory information for better performance. "The Internet was designed to be able to take outages, but when you take the root servers out, you don't know how long you can work without them," said Alan Paller, director of research at the SANS Institute, a security organization based in Bethesda, Md.
Although the Internet theoretically can operate with only a single root server, its performance would slow if more than four root servers failed for any appreciable length of time. In August 2000, four of the 13 root servers failed for a brief period because of a technical glitch.