On March 14th, 2017, Microsoft released a security bulletin titled Microsoft Security Bulletin MS17-010 – Critical also known as MS17-010. The advisory details vulnerabilities in the Microsoft Server Message Block 1.0 (SMBv1) server, and has been the vector for exploiting the ransomware cyber attack named WannaCry or Wanna Decryptor.

https://tools.cisco.com/security/center/content/CiscoSecurityResponse/cisco-sr-20170515