"Let's back up a minute to give you some quick background. Last fall, the FBI arrested six Estonian nationals who were charged with using malware and rogue DNS servers to hijack millions of computers worldwide.

At that time, Trend Micro's Feike Hacquebord called it the "biggest cybercriminal takedown in history." The company was one of several that worked with the FBI on the takedown, and described the scheme:

A variety of methods of monetizing the DNSChanger botnet [are] being used by criminals, including replacing advertisements on websites that are loaded by victims, hijacking of search results and pushing additional malware.Because the malware is so nasty — it's strong enough to wipe out a computer's anti-virus software — the FBI set up a safety net using government computers to prevent any Internet disruptions for users whose computers may be infected.

That safety net was set to go away in February, but the date has been extended to July 9 because the agency is concerned that not enough users are aware of the problem.

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Originally Posted by FBI To assist victims affected by the DNSChanger malicious software, the FBI obtained a court order authorizing the Internet Systems Consortium (ISC) to deploy and maintain temporary clean DNS servers. This solution is temporary, providing additional time for victims to clean affected computers and restore their normal DNS settings. The clean DNS servers will be turned off on July 9, 2012, and computers still impacted by DNSChanger may lose Internet connectivity at that time.