Windows XP was not especially vulnerable to Wannacry
 

Windows 7 machines might have been the problem

Windows XP was not as vulnerable to the WannaCry ransomware as many assumed.

Security experts at Kryptos research found that XP computers hit with the most common WannaCry attack just crashed and never managed to instal or spreading the ransomware.

http://fudzilla.com/news/43777-windo...le-to-wannacry