The Internet has been under a near constant Distributed Denial of Service (DDoS) attack since Monday, but has withstood the attack handily. DDoS attacks work by lobbing massive amounts of data at Internet-based servers from numerous locations simultaneously, an often crippling event that makes the servers unreachable by real users. But the current attacks, described as the worst ever, are aimed at the 13 root domain name system (DNS) servers that form the Internet's central address book. Curiously, they have had barely any effect at all, with no outages and few slow-downs. Matrix NetSystems reports that the reachability of the core DNS servers dropped just 6 percent at the height of the attack.

Part of the reason the Internet DNS servers responded so well is due to the distributed nature of the Internet, which doesn't have a centralized design that can be easily attacked. Also, even though the root DNS servers form the logical core of the Internet, they are rarely used by end user machines to locate Internet addresses, thanks to local DNS servers at ISPs, which can serve customers more quickly.

The Internet's root DNS servers are located around the world, though most of them are in the United States. Designated by single letters, A through M, the servers each field hundreds of millions of domain name requests each day.