If there were any lingering doubts about the importance of the Internet in American life and business, none remain.
As the World Trade Center towers toppled to the ground and the Pentagon lay burning, the network of networks proved true to its roots: The Internet stayed operational in the face of massive demand, with few outages, and became a communications lifeline for many of those caught in the maelstrom.
While cellular and public switched networks became temporarily overloaded and largely unusable immediately after the worst terrorist attack on U.S. territory, millions of people turned to the Web, e-mail and instant messages to find information and communicate with friends, family and business associates in the disaster zones.
"The Internet held up extremely well," said IP co-inventor Vinton Cerf. "We have more to do to make the Internet an even more robust and capacious platform for 21st-century communication, but I was very glad to see the system hold up under the significant loads experienced."
In addition to unusually heavy communications, many stricken companies were able to keep operating because of Internet-based data backup systems. Comdisco and SunGard, which provide networked computer backup, reported 110 disaster recovery requests. Other companies reverted to mirrored networks and kept running despite the chaos of the moment.
Still, the Net could have done better, said Tim Berners-Lee, inventor of the World Wide Web. "The Internet proved a very important medium for allowing people to exchange that 1-bit Im OK message with loved ones. However . . . it was very clear that the Net, like the phones, relies on central backbones, which can still be weak links. Id like to see the Web integrated with peer-to-peer protocols to make the whole infrastructure more resilient."
Indeed, as online users turned their attention away from television sets to computers, the Net sagged under the traffic load. Packet delivery slowed by half on Sept. 11 at 10:15 a.m. EDT - about an hour after the World Trade Center was hit - but returned to normal by midafternoon, according to network monitoring firm Keynote Systems. Major news sites were inundated and unreachable between 9 a.m. and 10 a.m. EDT, but their performance gradually improved during the day, as site operators dropped data-intensive advertising banners and graphics and trimmed down to just text.
The Internet performed admirably, but it wasnt the target of the attack. If it had been, the communications situation would likely have been far more grave, said technologist David Farber, a University of Pennsylvania professor. "There have always been certain [security] problems with the Net as it is," Farber said. "We know that it is somewhat vulnerable to attack. Not vulnerable to low-tech attack. [But] there are experts around the world who could cause a lot of problems."
One enemy proved to be diesel generators. Telehouse International Corp. of America, a company running a network exchange at 25 Broadway, advised its customers just after 5 p.m. EDT Thursday, Sept. 13, that its generator had failed due to overheating. Business continuity experts were also warning that backup diesel generators could shut down because of dust in the air.
The network disruptions, however, proved minimal. During the crisis, millions of Netizens did what now comes naturally: They logged on and used every means at their disposal to make contact with friends, family and business associates.
Salvatore Salamone, an IT consultant for Blue Cube who works from home on the Upper East Side of New York, had projects with 15 clients from around the country in progress when the trade towers were attacked. The assault came at a critical time, when those clients needed constant hand-holding and communication.
"I had a phone line, but a lot of people trying to reach me were being told the circuits were busy. I have three e-mail addresses, but I kept getting told the servers were busy," Salamone recalled. "But I did have instant messaging, and for some reason that seemed to work all right."
Salamone said he and his business partners had previously used AOL Instant Messenger (AIM) frequently for personal reasons, but rarely for business communications.
For telecommunications consultancy TeleChoice, AIM became a notification tool to inform people that fellow employees were alive and safe. Many of the firms 45 analysts were traveling, and those in the office were told to go home and telecommute after the tragedy.
"We knew that the traveling employees were OK as they booted up and came on instant messenger," said TeleChoice CEO Danny Briere. One of the unintended benefits of IM tools is the "presence" notification they provide. When members or "buddies" are online, their names are highlighted to illustrate the fact.
AOL Time Warner reported a surge in AIM usage, logging 1.2 billion messages - about 100 million more than usual. Officials of The Microsoft Network and Yahoo! said similar spikes occurred on their IM systems.
In the days after the attack, however, the FBI warned that companies should heighten their alerts to cyberattacks. And security firms followed with warnings that technologies like IM could make them vulnerable. RedSiren Technologies advised its clients to shut down all noncritical connections to the Internet -- including IM platforms, which could offer intruders a back door to critical systems.
Nevertheless, millions of e-mails and IMs brought reassurance, but not all. Somber corporate messages and Web sites informed the world of employees dead or missing. Technology companies were particularly hard hit, as the identities of hijacked aircraft passengers were released.
Among the known dead at press time were Edmund Glazer, chief financial officer and vice president of finance and administration at MRV Communications, a manufacturer of optical network components and systems; James E. Hayden, chief financial officer of e-commerce software company Netegrity; Steven D. Jacoby, an executive of Alexandria, Va., wireless company Metrocall; Daniel M. Lewin, co-founder of Akamai Technologies; and Phil Rosenzweig, Sun Microsystems director of Solaris software.
That list will no doubt grow, as companies that had operations or employees in the Twin Towers and the Pentagon continue head counts. Those companies include AT&T, Blue Sky Technologies, CNN, eMeritus Communications, General Telecommunications, Genuity, Kanebo Information Systems, Meganet Management Consultants, Sprint, Suggested Open Systems, Sun Microsystems, Verizon Communications and Xerox.
The Net also became part of the massive manhunt almost immediately. Shortly after the attacks, federal investigators contacted AOL and EarthLink to get undisclosed information to aid the investigation.
"They requested information from us and we complied on an immediate basis," said AOL spokesman Nicholas Graham, who declined to say what the investigators were looking for.
But as federal investigators fan out, civil libertarians are worried that personal privacy will be the next victim of the terrorists. Congress is already discussing the need to revisit newly relaxed regulations on encrypted products sold overseas. And some expect the FBIs unpopular Carnivore data surveillance program, which beat a hasty retreat last year, to resurface.
The Internet also became part of the nationwide effort to aid victims. AOL, CNN.com, The New York Times and other media sites posted blood bank locations and other public service announcements.
Federal agencies, however, fared poorly in using the Web, and most did not immediately post disaster information. Lacking any direct references to the crisis was FirstGov, which is supposed to be the primary government portal. The Department of Justice did not make reference to the attacks on its site until Wednesday, Sept. 12, with a statement from Attorney General John Ashcroft.
Amid the death, destruction and despair, the invisible strands of the Internet provided the ready means for rebuilding companies and communities that faceless terrorists hoped to destroy.
Other symbolic gestures, meant to rally patriotism by urging all Americans to do things such as help the stock market recuperate by buying stocks this week, were also forwarded through cyberspace.
AOL Time Warner Chairman Steve Case did what no other executive could. He sent a personal e-mail to 30 million citizens expressing his shock and condolences. "I am hopeful that soon a new perspective, and a new sense of hope, will start to emerge," he wrote to AOLs membership, "one that lifts our country and our spirits up, rather than succumbing to the terrorists goal of knocking us down and driving us apart.
"Rather than just watch the events unfold and be angry or frustrated, lets all do what we can now to help our country deal with the current challenge. And, in the months and years ahead, lets all recommit ourselves to build an even greater country," wrote Case.
Connie Guglielmo, Brian Ploskina, Max Smetannikov and Dan Luzadder contributed to this report.