DNSChanger is a family of Trojan which, as its name can tell, alters the DNS settings of infected computers (to force the computer to use a rogue DNS server) in order to redirect the user to malicious web sites or services. As a reminder, the DNS protocol allows systems to obtain the IP address of a server from its name: this process is called DNS resolution, and it happens for instance each time a user enters an URL in its favourite web browser.

Check System
http://www.dns-ok.de/