CNN went for a cut-down front page

The downloading of pages at the heaviest-hit sites slowed significantly at points through the day, but the internet as a whole proved to be a robust communication system compared with landline and mobile networks which were engaged for long periods of time.

The top US news networks all reported record figures for their online services. Technicians at MSNBC.com removed graphics from the site to allow users to access the news faster. CNN.com also posted a cut-down front page, which for a time was shorn of its usual video offerings, ads and other news stories.

And in Europe, the most visited online news operation, BBC News Online, also recorded record page impressions - although it too struggled at points through the day to meet all the requests being made for its content.

Performance improvement

Mike Smartt, editor-in chief of New Media at BBC News, said: "Traffic to BBC News Online increased to such an extent, as news of the first plane crashing into the World Trade Center came through, that very soon we were struggling hard to meet demand.

Frustrated users faced error messages

"We know that very many people could see the site throughout the afternoon - although it slowed. But others were disappointed. One factor appeared to be who your internet provider was."

Surfers unable to get into their favourite news sites went to search engines to find alternatives. Google directed users to radio and television. "Many online news services are not available, because of extremely high demand," a statement read on the popular site's home page.

Keynote Systems Inc, a consultancy that measures internet performance, said that in the early hours the news websites it tracked took longer to reach - nearly 13 seconds, compared with a daily average of five.

Keynote spokeswoman, Christina Mueller, said, "You could see visibly that performance became really bad after 0900 EST, when everyone was accessing news sites. There were no server crashes, but availability dropped dramatically." Performance improved by late afternoon."

Information thirst

Keynote made the observation that, worldwide, network traffic actually fell by 10% just after the first attack.

This view was supported in the UK where the London Internet Exchange - the centre through which most data to and from Britain is routed - saw overall net traffic fall by a similar percentage compared with a normal Tuesday.

"What we saw on the exchange was traffic dip by one gigabit - it was nowhere near where it would normally be for the time of day," marketing manager Vanessa Evans said.

It is a situation recognised by John K Thompson, a vice president with WhiteCross Systems, Inc, a consultancy that advises websites on how best to deal with major traffic events.

"People go to the news sites and find they cannot get online," he said. "The servers get swamped, people can't get the information they need immediately - they turn to the television; they turn to the radio. This is a phenomenon we have seen before."