Yesterday, March 16th, 2014, it was reported that google's public DNS server traffic was hijacked for 22 minutes, according to internet monitoring BGPmon.net's twitter feed. It reportedly affected networks in Brazil & Venezuela, redirecting millions of internet users, including many government agencies and financial institutions in those regions.
It is suspected that the hijackers used a well known vulnerability in the Border Gateway Protocol (BGP), BGP is used to exchange data between large service providers, if the hijackers utilized this vulnerability they could redirect traffic to a router they controlled.
This is not the first time Google's public DNS servers have been the victim of hijacking. In 2010, DNS traffic was redirected to Romania and Austria.