A dramatic story making the rounds claims that if "you don't have your computer malware free by July 9th the FBI will shut your computer down." As Techland points out, the story has roots in a small bit of reality but reporting on it has been a little bit overblown. The story originates all the way back to 2007, when malware called DNSChanger managed to infect millions of computers around the world. DNSChanger targeted Windows or Mac systems by manipulating Domain Name Servers (DNS) and DNS routing. When a computer became infected the malware would redirect DNS requests to servers controlled by an internet crime ring, which then served up web ads to users. Criminals using this malware managed to rake in millions of dollars. Eventually law enforcement in several countries figured out where the Malware came from and who was using it.
The FBI, working with Estonian officials, was able to track down the criminals behind the Malware - six Estonian nationals were arrested for the crime last November. The FBI also seized their servers but because the Malware had infected so many computers around the world, they decided to leave it running with the ads neutralized.
The FBI then secured a court order on March 12, 2012 that authorized the Internet Systems Consortium (ISC) to roll out and maintain temporary clean DNS servers. But the FBI can't run these servers forever (read: pay for them) so the plan is to shut them off on July 9, 2012. When that happens, DNS-related Internet activity on those computers still infected will cease to function.
If you want to see if your computer is infected with this malware, visit this FBI page and follow the instructions.