According to security researchers at Kasperksy Lab, roughly 98 percent of the PCs infected by the WannaCry ransomware were running different builds of Windows 7 operating system. The worst hit OS version – Windows 7 x64.
Windows 7, an operating system released in 2009, is still the most popular OS, as it’s running on 48% of desktop computers worldwide.
2008 R2 Server users were also hit quite hard, making up just over 1 percent of WannaCry infections.
Meanwhile, the number of infected computers running Windows XP was insignificant.
Microsoft had released a security patch for Windows 7 a few months before the WannaCry attack, so the infected computers would appear to be ones that hadn’t yet been updated. However, the patch for Windows XP was only released as an urgent update after this widescale incident.
According to Microsoft, Windows 10 is the only version of Windows OS that’s completely protected from WannaCry ransomware.