An attack on the Internet infrastructure yesterday may signal a hint of bigger things to come. The distributed denial-of-service (DDOS) attack that temporarily crippled -- but didn't take down -- two of the Internet's 13 Domain Name System (DNS) root servers was likely a test-run for a potentially larger and more disruptive attack, researchers say.

This was the latest in a series of DDOS attacks on DNS servers that began late last year, when DNS providers EveryDNS and EasyDNS each separately experienced attacks. Experts had predicted it was only a matter of time before botnet operators hit a bigger and higher-profile DNS target, and that's just what happened yesterday, they say.

The attackers targeted five of the Internet's DNS root name servers, using bots or zombified computers to execute the DDOS attack. Two of the root name servers eventually dropped 90 percent of their DNS query traffic, but the remaining servers kept the service operational. (See DNS Attacks on the Rise and DNS Service Under DDOS Attack .)

"Yesterday's attack was likely a precursor to a larger attack. The rise of DNS attacks in the last year has been worrisome," says David Ulevitch, CEO of OpenDNS, and founder of EveryDNS, both DNS services. "I believe the attack yesterday and the night before were tests to see how far someone could push the limits."

Ulevitch says the attackers split their attack capacity among a half-dozen or so targets. "Their overall DDOS capacity is significant, and is something to pay attention to," he says.

DNS root servers basically answer queries in the DNS infrastructure, which translates a computer's "human-readable" domain name into its machine-readable IP address.

The attackers used an army of bots from around the globe to hammer the servers with bogus and abnormally large DNS requests -- partially formed DNS messages of over 350 bytes each, according to a report from the ISC. The majority of the traffic came from nodes in Seoul (61 percent of the attack traffic) and Beijing (18 percent). Another 13 percent originated from nodes in San Francisco and another 7 percent elsewhere, according to ISC numbers.

The good news is investigators have been able to isolate many of the IP addresses of the offending machines and will therefore be able to shut down the botnet behind it all, Ulevitch notes. "The botnet operator will likely not be found, but at least he or she will have to start all over back at square one," he says.

Still, there's no way to be sure the attacker or attackers don't have other armies waiting in the wings to launch new and more aggressive attacks. This one only hit about a third of the DNS servers -- a larger attack using bigger armies could be more damaging to the Net.

"This attack is a strange one," says Craig Labovitz, director of engineering at Arbor Networks. "This has some people scratching their heads. It has some of the earmarks of a trial run, but it wasn't insignificant enough to fly under the radar. It was fairly large and disruptive."

But a scarier prospect is what such an attack could do if aimed at a business. The distributed and protected nature of the root servers kept the attack at bay. "How many midsize to large enterprises do you know that have 13 highly redundant data centers with highly redundant DNS servers?" says Paul Parisi, CTO for DNSstuff.com. "I'm worried about the corporate environment... This proves the technology is out there and can be leveraged autonomously.

"It would be trivial for an aggravated hacker to do serious damage to a company," Parisi continued. DDOS attacks are not only annoyances and service disruptions, but often are used as a distraction or cover for a "backdoor" attack, where an attacker can infect or steal data.

The saving grace for the DNS root servers in yesterday's attack was "anycasting" -- the streaming of DNS queries to multiple servers so they don't get lost or jammed up at a given server. "Anycasting is tremendously helpful, but it hasn't trickled into all of corporate America yet," Parisi says.

The servers were also bulked up and overbuilt to handle heavy loads, leaving end users blissfully ignorant of the attack. Several DNS root operators had added anycasting and redundancy to their servers in the wake of a similar, but more damaging, DDOS attack nearly five years ago.

But the underlying problem isn't really DNS: It's the pervasiveness of botnets, which automate and broaden these kinds of attacks. "Networks need to stop letting botnets run rampant across their backbones," OpenDNS's Ulevitch says. And "end users need to be running up-to-date antivirus software. Software manufacturers need to write better code. There are a hundred things that need to be done. And unfortunately, none of them are going to happen anytime soon."

Arbor's Labovitz says he's worried what the firepower of these botnets, many which contain ten or hundreds of thousands of machines, could to the Internet infrastructure if they were used against it. "The firepower is daunting to say the least," he says.

— Kelly Jackson Higgins, Senior Editor, Dark Reading