Following the recent WannaCry ransomware outbreak, Microsoft issued patches to the new unsupported Windows XP in order to rectify the vulnerabilities that WnnaCry exploited. Today, they have gone further issuing some further security patches as part of this month't Update Tuesday releases.
Information regarding the patches, which are available to users running Windows XP or later (including Windows 8, 8.1 and 10) through Windows Update, is available on the Windows blog. There's also further technical detail at Microsoft's Security TechCenter.
As always, my recommendation is to keep your software up to date, run only supported software (even though Microsoft has chosen to update Windows XP they weren't under an obligation to do so), and maintain tested offline backups so the damage done by a ransomware attack is mitigated.