From the USA.gov Blog:
DNS Malware: Is Your Computer Infected?:
DNS - Domain Name System - is an Internet service that converts user-friendly domain names, such as www.fbi.gov, into numerical addresses that allow computers to talk to each other. Without DNS and the DNS servers operated by Internet service providers, computers would not be able to browse web sites, send e-mail, or connect to any Internet services.
Criminals have infected millions of computers around the world with malware called DNSChanger which allows them to control DNS servers. As a result, the cyber thieves have forced unsuspecting users to visit fraudulent websites and made their computers vulnerable to other kinds of malicious software.
Check your computer’s DNS settings. If you’re a victim of the DNSChanger malware, you can register with the FBI.
Learn about DNSChanger malware and how it can affect your computer. (PDF)