Capabilities (Symbian Signed)/AllFiles Capability
The AllFiles capability gives read access to the whole filesystem. It also gives write access to most of the file system (except /sys and parts of /resource, which require TCB).
Notably, a program with AllFiles capability can read and write to any program's directory under /private.
This capability is very strictly controlled and it is not granted lightly. This capability is from manufacturer-approved category. To use it in your application you need to obtain a permission from device manufacturer directly. See Device Manufacturer Capabilities (Symbian Signed)
The /private directory may contain sensitive information, e.g. saved passwords. Modifying another program's configuration or data files directly can cause incorrect behaviour - in the worst case, the phone stops working.
The file server checks this capability when a normally restricted path is accessed.
The backup server needs AllFiles in order to be able to backup and restore /private. It is useful for debugging, so product creation tools often use it. In third-party applications it may be used for anti-virus software (though Symbian has little record of problems with viruses)