DNSChanger is a trojan designed to change DNS server address on computers that they are run on. This is done to redirect victims to fake websites that steal credit card information, logins and passwords for on-line banks and payment systems like PayPal.
The trojan modify some registry at TcpIp service and maybe it also adds some Windows service for monitoring...
To fix it
Option 1. Disable the DNS Client service (the service has no effect on client machine, it normally cache the DNS request to optimize)
Option 2. Download the CombFix http://download.bleepingcomputer.com/sUBs/ComboFix.exe and run, it'll automatically fix the issue for you.