According to security company Internet Identity (IID), half of Fortune 500 companies and government agencies have at least one computer infected with the DNS Changer malware.

"DNS Changer, which at its peak was installed on more than four million Windows PCs and Macs worldwide -- a quarter of them in the U.S. alone -- was the target of a major takedown organized by the U.S. Department of Justice last November," writes Computerworld's Gregg Keizer.

"The still-infected machines pose several problems, said experts," Keizer writes. "'Initially, DNS Changer was worrisome because it could redirect you from a safe location to a dangerous one controlled by criminals,' said Rod Rasmussen, the chief technology officer of IID in an emailed statement. 'However, the FBI temporarily fixed that. Now, the big worry is that machines that are still infected face a second vulnerability -- they are left with little if any security.' That's because DNS Changer also blocks software updates -- the patches vendors like Microsoft issue to fix flaws -- and disables installed security software."

Go to "Half of Fortune 500 firms infected with DNS Changer" to read the details.

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