Organizations that had not installed Microsoft's security update from April 2017 were affected by the attack.
[38] Those still running
unsupported versions of
Microsoft Windows, such as
Windows XP and
Windows Server 2003[39][40] were at particularly high risk because no security patches had been released since April 2014 for Windows XP (with the exception of one emergency patch released in May 2014) and July 2015 for Windows Server 2003.
[8] A
Kaspersky Lab study reported however, that less than 0.1 percent of the affected computers were running Windows XP, and that 98 percent of the affected computers were running Windows 7.
[8][41]