Roughly 98 percent of infected PCs were running a version of Windows 7, according to data released Friday by security firm Kaspersky Lab. About 1.5 percent of infections hit 2008 R2 Server clients, while Windows XP infections were "insignificant," Costin Raiu, director of research for Kaspersky Lab, said in a tweet.
"Those who are running our free antivirus software or have Windows Update enabled are protected," said a Microsoft spokesperson in an emailed statement. Microsoft is directing customers to its security blog for more information.
Update, 4:07 p.m. PT: Adds comment from Microsoft.