Due to the large-scale attack by the WannaCry ransomware, Microsoft has decided to release an important security update for Windows XP, Server 2003 and Windows 8. While the support for Windows XP and Server 2003 has ended, Microsoft has decided to be the good guy by providing patches and support.
WannaCry abuses a vulnerability in the Windows SMB.
Windows XP, Server 2003, and Windows 8 are no longer supported by Microsoft, and users are therefore vulnerable. The advice is to install the latest patches.