April 11, 2017—KB4015221 (OS Build 10240.17354)

Applies to: Windows 10

Improvements and fixes


This update includes quality improvements. No new operating system features are being introduced in this update. Key changes include:

  • Addressed issue where the copy operation fails when copying a file that has Encrypted File System (EFS) encryption to a share that is not encrypted by EFS.
  • Addressed an issue where CredentialGuard-enabled computers joined to Active Directory domains submit two bad logon attempts each time a bad password is provided during a Kerberos-based logon. Logons to Active Directory domains with arbitrarily low account lockout thresholds may be subject to unexpected account lockouts. For example, 2 logons with a bad password could result in an account being locked out if the account lockout threshold is set to 3 or 4.
  • Addressed issue that prevents the launch of the Delete Browsing History window in Internet Explorer.
  • Addressed a memory leak in Internet Explorer when hosting pages containing nested framesets that load cross domain content.
  • Addressed additional issues with updated time zone information, updates to the Access Point Name database and Internet Explorer.
  • Security updates to Scripting Engine, libjpeg image-processing library, Hyper-V, Win32k, Adobe Type Manager Font Driver, Internet Explorer, Microsoft Edge, Graphics component, .NET Framework,  Lightweight Directory Access Protocol, Windows kernel mode drivers and Windows OLE.

If you installed earlier updates, only the new fixes contained in this package will be downloaded and installed on your device.

Known issues in this update


Microsoft is not currently aware of any issues with this update.

How to get this update


This update will be downloaded and installed automatically from Windows Update. To get the stand-alone package for this update, go to the Microsoft Update Catalog website.

  • Update replacement information
    This update replaces the previously released update KB4016637.
  • File information
    For a list of the files that are provided in this update, download the file information for cumulative update 4015221. If you're installing a Windows 10 update for the first time, the package size for the X86 version is 505 MB and the package size for the x64 version is 1,104 MB.