This is the VOA Special English Technology Report.

A five-day Internet shutdown in Egypt failed to stop the protests that forced President Hosni Mubarak to resign. But it raised a technical question. Just how were Egyptian officials able to shut down Internet service in their country?

Craig Labovitz is chief scientist at Arbor Networks, an Internet security company in the American state of Michigan. Mr. Labovitz says the Internet is not as indestructible as people might think. He says there are points where the flow of computer traffic can be restricted.

CRAIG LABOVITZ: "From a technical standpoint, the popular imagination of the Internet is as a network that can survive nuclear wars, can't be stopped, is everything, everywhere. But the engineering realities are a lot more prosaic. In many countries there are a few natural bottlenecks, whether it be large data centers or right-of-ways."

Mr. Labovitz says his researchers tracked the Internet shut down in Egypt as it was being carried out. He explains that in Egypt, Internet users connect to the outside world through a small number of providers with international links.

CRAIG LABOVITZ: "Although there are a hundred or more providers within the country -- domestic providers -- there really are only four providers that maintain external links to the external world. And there's an even a smaller number of data centers where the fiber optics cross Egypt. So you really just need to turn off a handful of machines to have this type of disruption."

News reports suggested that the fiber optic links for those networks are even all housed in the same building.

Could a similar Internet shutdown take place in the United States? Craig Labovitz says that is less of a possibility because of a larger number of Internet providers and data centers.

Still, the recent shutdown in Egypt has raised new concerns about a proposal in the United States Congress. Critics say the legislation could make similar action possible in America.

The measure is known as the Protecting Cyberspace as a National Asset Act. Senator Joseph Lieberman of Connecticut first proposed the bill last June. Supporters say it would help protect the country's economic and national security from cyber attack. It would give the president the emergency power to shut down or seize parts of the nation's Internet in the event of a major threat.

Critics say the bill would give the president too much power. Some people call it the "Kill Switch Bill" -- an easy way to shut off the Internet. They say the government could use it to censor the Web and control the flow of information.