Hurricane Sandy doubled the average level of Internet outages in the United States and it took four days to bring it back to normal levels, U.S. scientists say. Computer scientists at the University of Southern California who track Internet outages throughout the world said when the hurricane hit the East coast, the outages doubled from 0.2 percent of the Internet being down -- about average -- to 0.43 percent, a USC release reported Tuesday. \"On a national scale, the amount of outage is small, showing how robust the Internet is,\" John Heidemann of the USC Information Sciences Institute said. \"However, this significant increase in outages shows the large impact Sandy had on our national infrastructure.\" During the hurricane the researchers sent tiny packets of data known as \"pings\" to networks and waited for \"echoes\" or responses, a method that can provide a statistically reasonable picture of when parts of the Internet are active or down. The researchers were also able to pinpoint locations of outages, detecting a spike in outages in New Jersey and New York after Sandy made landfall. Knowing scale and location of outages could guide Internet service providers in allocating resources to respond to disasters, the researchers said. \"We are working to improve the coverage of our techniques to provide a nearly real-time view of outages across the entire Internet,\" Heidemann said. \"We hope that our approach can help first responders quickly understand the scope of evolving natural disasters.\"