The rogue DNSChanger servers will shut down on July 9 2012, meaning users have only a month to scan their PCs for faulty DNS settings and possibly prevent being cut off from the internet. Facebook began notifying users infected with the malware via a warning message saying, Your computer or network might be infected Only those who are part of the malware botnet are prompted with the message and a clear set of instructions to clean up DNS settings. A DNSChangers Removal Tool has been created to scan PCs infected and automatically fix any settings that it might have corrupted.”]
Source: https://www.bitdefender.com/blog/hotforsecurity/facebook-issues-warnings-to-dnschanger-victims/