How does Windows 7 built-in Guest account can write into HKLM key?

I'm not sure what went wrong in my Windows 7 permissions configuration, but I just discovered that while being logging in as a Guest account I can add and remove keys from the HKEY_LOCAL_MACHINE\SOFTWARE registry key. Where do I need to look to change that? (Apart from disabling the Guest account.)

PS. I've been testing some backup programs lately and even though they're all now uninstalled, one of them might have done this.

PS2. I checked and my UAC is enabled.

Hello,

To solve this you need to revoke Guest's access to the HKLM key. Follow these instructions:

1. Login as an administrator.
2. Open the Registry Editor.
3. Right click on HKEY_LOCAL_MACHINE.
4. Choose "Permissions...".
5. Choose "Everyone", and uncheck the "Full Control" box.
6. Tick the "Full Control" box for users that you do want to allow to change that key.

techhead287

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Thanks. In that case "Everyone" has only read permission.