Overview
Some users repeatedly see a prompt to type the challenge phrase "A1B2C3" at sign-in. It is a Windows Hello safeguard, but when it keeps appearing it usually means your PIN/credential store (the NGC folder) is corrupted. This guide shows how to get past it and stop it recurring.
Windows can repeatedly ask for the A1B2C3 challenge phrase.
Warning: One fix involves deleting the Windows Hello (NGC) credential folder. Back up important data and know your Microsoft account password first, since you will re-create your PIN afterward.
Key Takeaways
- A1B2C3 is a Windows Hello verification prompt; recurring prompts indicate corrupted PIN data.
- First, type A1B2C3 exactly to get into Windows.
- Reset the PIN via "I forgot my PIN".
- If it persists, reset permissions on and clear the NGC folder, then create a fresh PIN.
Step 1 — Get Past the Prompt
1. When prompted, type A1B2C3 exactly (the literal challenge phrase) to continue signing in.
2. Or click Sign-in options and use your password or another method.
The A1B2C3 challenge phrase prompt.
Step 2 — Reset Your PIN
1. Open Settings > Accounts > Sign-in options > PIN (Windows Hello).
2. Click "I forgot my PIN".
3. Verify with your Microsoft account password and set a new PIN.
4. Restart and check whether the prompt returns.
Step 3 — Reset and Clear the NGC Folder (If It Persists)
Warning: This removes all Windows Hello PINs/biometrics for the device; you will set them up again.
1. Open Command Prompt as administrator.
2. Take ownership/reset permissions on the NGC folder: takeown /f C:\Windows\ServiceProfiles\LocalService\AppData\Local\Microsoft\Ngc /r /d y, then icacls on the same path granting administrators full control.
3. Delete the contents of that Ngc folder (not the folder itself).
4. Restart, then go to Sign-in options and create a new PIN — Windows rebuilds the credential files.
Troubleshooting
Problem: A1B2C3 does not let me in.
Solution: Use Sign-in options and your account password instead, then reset the PIN from Settings.
Problem: You cannot access the Ngc folder.
Solution: Use takeown and icacls as administrator to reset ownership/permissions before clearing its contents.
Problem: The prompt returns after resetting the PIN.
Solution: Clear the NGC folder contents (Step 3) and create a fresh PIN; corrupted credential files are the usual cause.
Problem: You are on a work/school device.
Solution: Your organisation may manage Windows Hello. Contact IT rather than clearing the credential store yourself.
Conclusion
The recurring A1B2C3 prompt points to a corrupted Windows Hello PIN store. Get in with the phrase or your password, reset the PIN, and if needed clear the NGC folder and create a fresh PIN to stop it for good.
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