Hundreds of thousands of Internet servers are at risk of an attack that would redirect unknowing Web surfers from legitimate sites to malicious ones. In a scan of 2.5 million so-called Domain Name System machines, which act as the White Pages of the Internet, security researcher Dan Kaminsky found that about 230,000 are potentially vulnerable to a threat known as DNS cache poisoning.

"That is almost 10 percent of the scanned DNS servers," Kaminsky said in a presentation last week at the Black Hat security event in Las Vegas. "If you are not auditing your DNS servers, please start," he said.

The motivation for a potential attack is money, according to the SANS Internet Storm Center, which tracks network threats. Attackers typically get paid for each spyware or adware program they manage to get installed on a person's PC.

Information lifted from victims, such as social security numbers and credit card data, can also be sold. Additionally, malicious software could be installed on a PC to hijack it and use it to relay spam.

The DNS servers in question are run by companies and Internet service providers to translate text-based Internet addresses into numeric IP addresses. The cache on each machine is used as a local store of data for Web addresses.