File Explorer Preview Pane Security Block (False Positive)
Status: Partially Fixed | First Reported: October 2025
The Problem: KB5066835 and later updates block File Explorer previews with false warning: “The file you are attempting to preview could harm your computer” even for harmless PDFs/Docs
Registry Workaround (Undocumented):
cmd
Copy
# Disable Mark-of-the-Web blocking for preview handlers
reg add "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Attachments" /v SaveZoneInformation /t REG_DWORD /d 1 /f
# Clear existing MOTW streams (run as admin)
streams -d -s "C:\Users\%username%\Downloads"
# Note: Requires Sysinternals Streams tool