As schools increasingly rely on the internet for their mission-critical operations, the concern among educators for potential service disruptions increases, too. This week, tech-savvy educators were following with keen interest the ongoing investigation into one of the most serious attacks on the internet yet.

The White House on Oct. 23 sought to allay concerns about an unusual attack against the 13 computer servers that manage global internet traffic, stressing that disruption was minimal and that the Federal Bureau of Investigation is working to trace the attackers.

Most internet users didn't notice any effects from the Oct. 21 attack, because it lasted only one hour and because the internet's architecture was designed to tolerate such short-term disruptions, experts said.

The White House said it was unclear where the attack originated, who might be responsible, or whether the attack could be considered cyber-terrorism.

"We don't know. We'll take a look to see if there are any signs of who it may or may not be," spokesman Ari Fleischer said. "I'm not aware there's anything that would lead anybody in that direction. History has shown that many of these attacks actually come from the hacker community.

But that's why an investigation is under way." The FBI's National Infrastructure Protection Center and agents from its cyber-crime division were investigating, FBI spokesman Steven Berry said.

Civilian technical experts assisting with the investigation, speaking on condition of anonymity, said the FBI was reviewing electronic logs of computers used in the attack to determine the origin of those responsible.

"It's the nature of these things that they're never easy to untangle, and yet sometimes there are clues left behind," said Steve Crocker, chairman of an advisory committee on the security and stability of these servers for the Internet Corporation for Assigned Names and Numbers.

Another expert, Paul Mockapetris, the chief scientist at Nominum Inc., said those responsible appeared to use generic "ping flood" attack software that had been installed on computers across the globe using many different internet providers. His company provides consulting advice to some of the organizations operating the servers.

"It was a fairly large attack, but it doesn't look to be an attack designed to do maximum damage," said Richard Probst, a vice president at Nominum. "Either it was a wake-up call, or a publicity stunt, or a probe to understand how the system works."

In so-called "denial of service" attacks, hackers traditionally seize control of third-party computers owned by schools, corporations, and even home users and direct them to send floods of data at pre-selected targets.

The Oct. 23 attack was notable because it crippled nine of the 13 servers around the globe that manage internet traffic. Seven failed to respond to legitimate network traffic and two others failed intermittently during the attack, officials confirmed.