I recently installed Windows 11 25H2 and noticed a strange issue when enabling the built-in Administrator account.
When I activate the built-in Administrator account and log in with it, Windows Defender (Windows Security) becomes extremely slow to open. After clicking it, the window stays completely white for up to 10 seconds before finally loading and displaying the information.
However:
If I create a new user and add it to the Administrators group, Windows Defender opens normally.
The issue only happens when using the built-in Administrator account.
If I disable the built-in Administrator account and use a regular user with administrative privileges, everything works correctly.
I also tested the following:
I created a new user and added it to the Administrators group → Windows Defender opens normally.
Then I disabled UAC (User Account Control) for this new administrator account to avoid elevation prompts.
After disabling UAC, Windows Defender becomes slow again and shows the same white screen delay (just like when using the built-in Administrator account).
So it seems the issue is related to running without UAC elevation prompts.
Additionally:
On Windows 11 23H2, this problem does not occur.
The issue only started happening from version 24H2 onward (including 25H2).
Summary of behavior:
✅ New admin user with UAC enabled → Windows Defender opens normally
❌ Built-in Administrator account (UAC effectively disabled) → Defender very slow (white screen ~10 seconds)
❌ New admin user with UAC disabled → Same slowdown occurs
✅ Windows 11 23H2 → No issue
❌ Windows 11 24H2 and 25H2 → Issue occurs
command:
reg add "HKLMSOFTWAREMicrosoftWindowsCurrentVersionPoliciesSystem" /v EnableLUA /t REG_DWORD /d 0 /f
How do I fix this so that Defender doesn’t have this disparity in performance between the various accounts?
