The Georgia Tech and Google researchers estimate that as many as 0.4%, or 68,000, open-recursive DNS servers are behaving maliciously, returning false answers to DNS queries. They also estimate that another 2% of them provide questionable results. Collectively, these servers are beginning to form a "second secret authority" for DNS that is undermining the trustworthiness of the Internet, the researchers warned.
"This is a crime with few witnesses," said David Dagon, a researcher at Georgia Tech who co-authored the paper. "These hosts are like carnival barkers. No matter what you ask them, they'll happily direct you to the red light store, or to a Web server that does nothing more than spray your eyeballs with ads."
Attacks on the DNS system are not new, and online criminals have been changing DNS settings in victim's computers for at least four years, Dagon said. But only recently have the bad guys lined up the technology and expertise to reliably launch this particular type of attack in a more widespread way. While the first such attacks used computer viruses to make these changes, lately attackers have been relying on Web-based malware.