UsrClass.dat C:\Users\<utilisateur>\AppData\Local\Microsoft\Windows\UsrClass.dat

Registry hive for the user's HKCU\Software\Classes: file associations and COM registrations specific to the profile; locked during the session.

Updated on 12 November 2026 By AltF4 Formation

What it’s for

UsrClass.dat is the hive file that backs the user’s HKEY_CURRENT_USER\Software\Classes key. It complements NTUSER.DAT. It contains user-specific class data: file type associations, per-user COM registrations and Explorer interface settings. When the profile loads, it is mounted under HKEY_USERS\<SID>_Classes.

What it contains

A binary file in registry hive format, with transaction files (UsrClass.dat.LOG1, .LOG2) in the same folder. It is hidden and a system file. Depending on use, it may also keep traces of folder navigation (Explorer view settings).

Risks and best practices

A corrupted or missing UsrClass.dat breaks file associations, crashes Explorer or prevents sign-in. Do not swap the file: for a corrupted profile, create a new profile and migrate the data.
The file is locked while the user is signed in. To open it, load the hive with Regedit or reg load from another session, on a copy, after a backup.
It keeps traces of user activity (Explorer view settings, for example), so treat any copy as personal data.
Back up the whole profile rather than this file alone.

Useful commands

# File presence and date (hidden, read-only)
Get-Item -Force "$env:LOCALAPPDATA\Microsoft\Windows\UsrClass.dat*" | Select-Object Name, Length, LastWriteTime, Attributes

# Hives loaded for signed-in users
Get-ChildItem Registry::HKEY_USERS | Select-Object Name

# Read a class key of the current user (example: .txt association)
Get-ItemProperty 'HKCU:\Software\Classes\.txt' -ErrorAction SilentlyContinue

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