The raw data
Looking at the plain numbers, the terrorist attacks had a devastating effect and revealed the limits of the Internet back in 2001.
According to Keynote Systems, a company that measures Internet performance, especially search engines, government and news sites were impacted. Google was up and running, but told news seekers in a statement on its homepage that "many online news services are not available, because of extremely high demand." Keynote said that the websites of the New York Times, ABC News and CNN showed 0% availability in the first hour following the first plane crash. Traffic overload made the sites virtually unreachable: Even on 12 September, users had to wait 100 seconds to get a response fro the New York Times website. USAToday.com had an 18% availability and MSNC 22%. The average response time of the top 40 business websites monitored by Keynote was 12.9 seconds on 9/11 - up from a typical 2.5 seconds.
Some government websites, including the properties of the FBI and CIA showed similar degradation: According to Keynote, the response time of fbi.gov was 126.9 seconds on 9/11; cia.gov was measured at 7.59 seconds.
The experts at Keynote explained that the slowdown of the Internet was the result of increased traffic, not of infrastructure destruction. Despite the vast damage done to the telecommunication networks, Internet data traffic wasn't impacted: The World Trade Center housed countless Internet endpoints, but no "peering points" - junctions that exchange data between major data networks. "The performance impact we're seeing this week indicates massive Internet traffic, particularly from users at work following current events online, that is apparently affecting performance overall. In fact, the immediate and dramatic decline in availability of the major news sites is the kind of performance effect we see characteristic of Denial of Service attacks," Keynote wrote in a press released on 11 September 2001.
CNN.com, one of the major destinations of people seeking information about the attacks, said that it saw record traffic. Between 9am and 10am EST, the site counted more than nine million visitors, which compared to an average of 11 million visitors to CNN on a typical day back in 2001. CNN.com registered 162 million visitors on that Tuesday - and 300 million the day thereafter.
MSNBC.com said it noticed a 10x in traffic on 9/11. Close to 300,000 people were accessing the site immediately after the attacks, the company said.
According to a report of the Pew Internet & American Life Project released on 15 September 2001, 81% of Americans said that they got most of their information from TV. About 11% of Americans said they got most of their information from radio only 3% of Internet users indicated they got most of their information about the attacks and the aftermath from the Internet. But the organization indicated that 30 million American adults attempted to get online news of the attacks on 9/11. About 43 percent said they had "some" or "a lot" of problems reaching the sites they wanted to see. Of those, 41 percent kept trying to access the same site until they finally reached it; 38 percent went to other sites and 19 percent gave up.
With hours passing, websites got more creative in coping with the flood of visitors. From adding web servers, shifting capacities to sister sites, removing eye-candy from front pages and utilizing other information tools such as newsletters, capacity came back online within a few hours: Websites were able to provide text and multimedia information on events, emergency contacts and databases. The Internet's reliability remained the target of critics, but there were positive notes as well: Keynote's senior director Bill Jones said that the terrorist attacks resulted in the "worst ever" drop in availability of the Internet, but argued that lag times were acceptable: "The Internet is performing every bit as it was designed. The Internet has come of age as a result of this disaster," Jones said in an interview with Computerworld.