Symptoms

  • Windows Update reaches a percentage then fails with 0x800705B4.
  • Microsoft Defender will not turn on or update its definitions.
  • Optional feature installs time out with the same code.

What causes 0x800705B4

  • A slow or unstable internet connection during the download.
  • A third-party antivirus running alongside Defender and blocking it.
  • Corrupt Windows Update cache.

How to fix it

  1. Pause or uninstall any third-party antivirus temporarily, then retry the operation.
  2. Run the Windows Update troubleshooter and reset the update components (command below).
  3. Restart and retry the update on a wired or strong Wi-Fi connection.

Terminal / CLI command

net stop wuauserv && net stop bits && net start wuauserv && net start bits

Elevated Command Prompt.

How to confirm the fix: The update or Defender operation completes without timing out.

Prevent it from coming back

Run only one real-time antivirus, and start large updates when you have a stable connection.