From the FBI site:
DNS (Domain Name System) is an Internet service that converts user-friendly domain
names into the numerical Internet protocol (IP) addresses that computers use to talk to
each other. When you enter a domain name, such as http://www.fbi.gov, in your web browser
address bar, your computer contacts DNS servers to determine the IP address for the
website. Your computer then uses this IP address to locate and connect to the website. DNS
servers are operated by your Internet service provider (ISP) and are included in your
computer’s network configuration. DNS and DNS Servers are a critical component of your
computer’s operating environment—without them, you would not be able to access
websites, send e-mail, or use any other Internet services.
Criminals have learned that if they can control a user’s DNS servers, they can control what
sites the user connects to on the Internet. By controlling DNS, a criminal can get an
unsuspecting user to connect to a fraudulent website or to interfere with that user’s online
web browsing. One way criminals do this is by infecting computers with a class of malicious
software (malware) called DNSChanger. In this scenario, the criminal uses the malware to
change the user’s DNS server settings to replace the ISP’s good DNS servers with bad DNS
servers operated by the criminal. A bad DNS server operated by a criminal is referred to as
a rogue DNS server.
The FBI has uncovered a network of rogue DNS servers and has taken steps to disable it.
The FBI is also undertaking an effort to identify and notify victims who have been impacted
by the DNSChanger malware. One consequence of disabling the rogue DNS network is that
victims who rely on the rogue DNS network for DNS service could lose access to DNS
services. To address this, the FBI has worked with private sector technical experts to
develop a plan for a private-sector, non-government entity to operate and maintain clean
DNS servers for the infected victims. The FBI has also provided information to ISPs that can
be used to redirect their users from the rogue DNS servers to the ISPs’ own legitimate
servers. The FBI will support the operation of the clean DNS servers for four months,
allowing time for users, businesses, and other entities to identify and fix infected
computers. At no time will the FBI have access to any data concerning the Internet activity
of the victims.
It is quite possible that computers infected with this malware may also be infected with
other malware. The establishment of these clean DNS servers does not guarantee that the
computers are safe from other malware. The main intent is to ensure users do not lose DNS