In a presentation at the Black Hat conference last week, security researcher Dan Kaminsky argued that domain name system (DNS) servers represent a broad vulnerability in the Internet. Kaminsky said that of2.5 million DNS servers he tested, nearly 10 percent could be susceptible to so-called DNS cache poisoning. In total, about 9 million DNS servers are operating globally. DNS servers translate typed URLs into numbers necessary to locate Web sites. In cache poisoning, legitimate numeric Web addresses are replaced, causing users to be redirected to sites of the hacker's choosing. Often, users are sent to Web sites that install malware or that deceive users into disclosing personal information, which can then be used in identity theft.Incidents of cache poisoning have disrupted Internet service in the past, including this March, when users trying to access CNN.com and MSN.com were sent to sites that installed spyware. Security experts advise operators of DNS servers to audit their machines and make sure they configure them in the safest manner possible.