More on events in Egypt
According to internet monitoring firm Renesys, shortly before 2300 GMT on 27 January virtually all routes to Egyptian networks were simultaneously withdrawn from the internet's global routing table.
That meant that virtually all of Egypt's internet addresses were unreachable.
Egyptian authorities seem to have manged this by shutting down official Domain Name Servers (DNS) in Egypt. These act as address books and are consulted by web browsing software to find out the location of a site a user wants to visit.
Messages circulating in Egypt pointed people towards unofficial DNS servers so they could get back online.