To figure out whether you've been infected with DNSChanger, just point your Web browser to one of the (admittedly amateur-looking) websites that Internet security organizations maintain across the globe. The link above will take you to a DNS Changer Check-Up page in the United States that the DNS Changer Working Group maintains; if you live outside the United States, you can consult the FBI's list of to find an appropriate service for your region.

Unfortunately, if your router is infected, those websites will think that your PC is infected, even though it may be clean; worse, if your ISP redirects DNS traffic, your PC may appear to be clean even though your DNS settings may have been maliciously altered. If you want to be certain that your PC is free of DNSChanger malware, you need to manually look up the IP addresses of the DNS servers that your PC contacts to resolve domain names when browsing the Web.

To look up which DNS servers your Windows 7 PC is using, open your Start menu and either run the Command Prompt application or type cmd in the Search field. Once you have a command prompt open, type ipconfig /allcompartments /all at the command line and press Enter. A big block of text should appear; scroll through it until you see a line that says 'DNS Servers', and copy down the string(s) of numbers that follow (there may be more than one string here, meaning that your PC accesses more than one DNS server).

It's even easier for Mac OS X users to determine the IP addresses of the DNS servers that their PC uses. Open the Apple menu (usually located in the upper-left corner of the screen) and select System Preferences. Next, click the Network icon to open your Network Settings menu; navigate to Advanced Settings, and copy down the string(s) of numbers listed in the DNS Server box.