I was watching WCNC news this morning, and saw them covering a new Windows virus that is coming out, and is spreading so fast that you might not even know that you have it.
The virus is dubbed DNS-Changer. It does exactly what it is named. It modifies DNS queries to point to malicious or generally harmful websites.
So to make sure that you don't have this virus, visit http://www.dcwg.org/. There you can find plenty of info about the virus group, and the latest one.