Microsoft delayed its regular Patch Tuesday set of security fixes for its Windows and Office products earlier this month. The software maker blamed an unspecified “last minute issue,” and pushed back the set of patches a whole month. Microsoft was expected to patch a zero-day flaw in the company’s file sharing protocol, SMB, with its February patches, but the issue remains unfixed.

In a surprise out-of-band release last night, Microsoft issued a critical security fix to rectify an issue with Adobe’s Flash Player on Windows 8.1, Windows Server 2012, Windows Server 2012 R2, Windows RT 8.1, Windows 10, and Windows Server 2016. The patch requires a restart, and fixes a problem that could lead to remote code execution. It's a serious issue, so check Windows Update and install the patch immediately.

Microsoft hasn’t provided any information on why this security patch was released outside of Patch Tuesday, or whether any other patches will arrive before the next round of patches on March 14th.