Applications written with the assumption that the user will be running with administrator privileges experienced problems in earlier versions of Windows when run from limited user accounts, often because they attempted to write to machine-wide or system directories (such as "Program Files") or registry keys (notably HKLM) UAC attempts to alleviate this using "File and Registry Virtualization", which redirects writes (and subsequent reads) to a per-user location within the user's profile. For example, if an application attempts to write to “C:\program files\appname\settings.ini” and the user doesn't have permissions to write to that directory, the write will get redirected to “C:\Users\username\AppData\Local\VirtualStore\Program Files\appname\.”