Once you know the IP addresses of the DNS servers that your PC is using, head over to the and enter those addresses into the search box. Press the big blue Check Your DNS button, and the FBI's software will tell you whether your PC is using rogue DNS servers to access the Internet.

If your PC is infected with DNSChanger, you'll have to do some intensive work to get rid of it. DNSChanger is a powerful rootkit that does more than just alter DNS settings; if you've been infected with DNSChanger, your safest course is to back up your important data, reformat your hard drive(s), and reinstall your operating system. For more information, consult our guide to .

If you're leery of reformatting your entire PC, you can try rooting out the DNSChanger rootkit with a free rootkit removal utility such as Kaspersky Labs' . As the name implies, Kaspersky released the program to help PC owners seek and destroy the TDSS rootkit malware, but it also detects and attempts to eliminate DNSChanger and many other forms of rootkits.

If the infected PC is on a network, you'll have to check every other PC on the network for signs of infection, and then check your router's settings to ensure that it isn't affected (DNSChanger is programmed to change router DNS settings automatically, using the default usernames and passwords of most modern routers). To do this, copy down your router's DNS server IP addresses (located in your router's settings menu; read "" for more information) and check them against the FBI's IP address database mentioned above. If your router is infected, reset the router and confirm that all network settings are restored to the manufacturer's defaults.