hundreds of thousands of people around the world could lose access to the internet as a result of DNSChanger. It has been estimated that the malware affects almost 20,000 computer users in the UK alone.
In November 2011, the FBI and Estonian authorities arrested the leaders of an ad-fraud related botnet called DNSChanger. The botnet altered DNS server settings on the infected computers in order to conduct ad-fraud schemes. Over 500,000 computers were infected at one point. As of June 11th there were still 300,000+ unique IP addresses that connect to the DNS servers being run on behalf of the FBI.
The US courts have authorised the FBI's servers until July 9th. So after this date the infected computers can’t search the web before the DNS settings are changed. F-Secure has created a script-based tool to that can be used to reset the problematic DNS settings on infected computers.
You can find out if your computer infected here
and learn all about it here