According to data released today by Kaspersky Lab, roughly 98 percent of the computers affected by the ransomware were running some version of Windows 7, with less than one in a thousand running Windows XP. 2008 R2 Server clients were also hit hard, making up just over 1 percent of infections.
Windows 7 is still by far the most common version of Windows, running on roughly four times as many computers as Windows 10 worldwide. Since more recent versions of Windows aren’t vulnerable to WannaCry, it makes sense that most of the infections would hit computers running 7. Still, the stark disparity emphasizes how small of a role Windows XP seems to have played in spreading the infection, despite early concerns about the outdated operating system.