Update your Windows OS

This month's update fixes a ton of security bugs, including at least one that is being exploited by Ransomware:

Microsoft patched 97 security flaws today for April's Patch Tuesday including one that has already been found and exploited by miscreants attempting to deploy Nokoyawa ransomware.

Redmond deemed seven of the now-patched vulnerabilities "critical" and the rest merely "important."

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As Microsoft warned: "An attacker who successfully exploited this vulnerability could gain SYSTEM privileges." 

For non-technical folks, that translates as Game-Set-Match.  Run Windows Update - it will tell you if it ran automatically which would be great but you want this update.