As protesters take to the streets in Egypt, the government has reportedly shut down the Internet. How does that work? Does Egypt’s Internet have an on/off switch?

No. While we don’t know exactly how the Egyptian government choked off Internet access, there’s no centralized red button that the government—or anyone—can push to turn it off. Evidence suggests a government official called Egypt’s four biggest Internet service providers—Link Egypt, Vodafone/Raya, Telecom Egypt, and Etisalat Misr—and told them to halt connections. (Vodafone has said it cooperated because the regime has the legal authority to order such a halt.) An engineer at each ISP would then access the ISP’s routers, which contain lists of all the IP addresses accessible through that provider, and delete most or all of those IP addresses, thus cutting off anyone who wants to access them from within or outside the country. That doesn’t mean each ISP had to physically power down their computers; they simply had to change some lines of code.

Egypt didn’t shut down the entire Internet. About 93 percent of Egyptian networks have been disabled, according to Renesys, a company that monitors global Internet activity. One major ISP, Noor Group, is still up and running. Perhaps not coincidentally, Noor happens to host Egypt’s stock exchange. Web connections used by the government and military are also likely still operating on their own private ISPs. Some Egyptian users might also be able to use old-fashioned dial-up connections.

Egypt may be the largest country to have cut off the Internet, but it’s not the only one. Burma orchestrated a shutdown in 2007 to coincide with a violent crackdown on protesters, as did Nepal when its government declared martial law in 2005. Other countries, like Iran, Brazil, and China, have deliberately slowed down the Internet or blocked certain Web sites. But filtering Web traffic based on search terms or blacklists—which Internet users can usually get around, using mirror sites or proxy servers—is a less blunt instrument than cutting it off entirely.

Withholding the Internet in Egypt is relatively easy, compared with other more democratic countries. For one thing, there are only four major ISPs, each of which has relatively few routers connecting them to the outside world. By comparison, anyone who wanted to shut down the Internet in the United States would have to deal with many different companies. And whileEgypt can legally disable telecom companies by executive decree, American companies might fall under various regulatory umbrellas that limit the government’s power to disrupt communication channels. Members of Congress have proposed creating a “kill switch” that would shut down the Internet at the push of a button in the case of a “cybersecurity emergency,” but erecting such a blockade would be logistically difficult.

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