Microsoft made the very unusual release to help stem the ransomware outbreak.
WannaCry ransomware exploded over the weekend and spread like a worm to infect more than 200,000 systems across 150 countries around the world, according to Europol. In response, Microsoft took the emergency step to release a patch for no longer supported versions of Windows.
The WannaCry ransomware—also known as Wanna Decryptor, WannaCrypt and WannaCryptor—emerged on Friday and is based on the EternalBlue exploit of Windows Server Message Block (SMB) v1 found in a recent dump of NSA cyberweapons. Microsoft had released a patch for supported systems in the March 2017 Patch Tuesday updates with bulletin MS17-010.
However, the WannaCry infections spread fast among legacy systems, especially in healthcare organizations, and prompted Microsoft to take "the highly unusual step of providing a security update for all customers to protect Windows platforms that are in custom support only, including Windows XP, Windows 8 and Windows Server 2003," according to a blog post from Friday.