One week after WannaCry's attack, the analysis of the data collected shows that the most malicious software was Windows 7 and not Windows XP, according to Kaspersky security firm.
Specifically, over the 60% + 31% of the computers hit by WannaCry ran 64 or 32 bits (respectively) of the Windows 7 operating system.
Ironically, Windows 7 had to be safe against WannaCry, as Microsoft had released security patches since March of 2017. Also, we should not forget that the operating system is supposed to still be supported.
On the other hand, seeing Windows 7 as the most influenced operating system by WannaCry malware shows it makes sense. Because if you think it's the world's top PC operating system with a market share of almost 50% it seems to be the right percentage.
This means that almost 1 on 2 desktop systems run with Window 7.
It is worth mentioning that Window 7 is pirated in many systems out there, especially in countries like China and Russia, which still use non-genuine operating system replicas.
This has the effect of not being able to update them every month, while many users have completely blocked updates to avoid checking for genuine product keys.
Note that Windows 7 will continue to be supported by January of 2020, so genuine systems with this operating system will still receive updates for almost 3 years.