When it comes to security, the Domain Name System has suffered from benign neglect. But old and emerging threats to the system that allows computer users to find Web sites will force technology managers to strengthen their DNS infrastructures, experts say.

DNS is the worldwide system for regulating Internet host names. It was designed to be efficient and easy for trusted users, but it lacks inherent security mechanisms, experts say. Moreover, many organizations run DNS services on general-purpose servers that are susceptible to vulnerabilities that hackers can exploit.

Some attacks can be subtle and hard to notice, said Marty Lindner, a senior member of the technical staff at the CERT Coordination Center. For example, domain cache poisoning allows hackers to redirect Web users to computers that they specify rather than the intended destinations.

Symantec's latest Internet Security Threat Report, issued in March, identifies Domain cache poisoning as one of the top attacks on government networks. The company bases its biannual update on cyberthreats on data gleaned from a broad sample of its worldwide private- and public- sector customers. Domain cache poisoning is not as prevalent in the private sector, Symantec officials say.

DNS is a hierarchy composed of domains — 265 so far, including .com, .org and country codes. DNS root and name servers act as address books, associating names of Web sites with IP addresses, said Jason Brvenik, a security engineering manager at Sourcefire, which sells equipment that detects and prevents intrusions.

Some organizations are not paying a lot of attention to DNS attacks because the system is "not being exploited in such a way that people are losing sleep over it," Lindner said. That's partly because attackers are doing so much damage in other ways that many companies don't think it's worth protecting DNS, he said.

Another factor is that the "damage by DNS attacks is not sufficiently big for [some] people to worry enough about it," said Johannes Ullrich, chief research officer at the SANS Institute.

Attacks are moving from Web servers that millions of people rely on to specific applications on a few servers that affect one or two companies, Ullrich said.

Playing the odds, most systems administrators don't protect against DNS attacks, and even companies that have been hit don't do much more than install software patches, Ullrich said. "Everyone is hoping it's not them," he said.