The list of virtual directories that cannot be deleted is specified by your device manufacturer. There is no way for end users to alter this list.
Caution: It is possible to change other settings for protected virtual directories like WebAdmin, such as the allowed users and the level of authentication required. Incorrectly configuring these options may cause you to be blocked out of accessing the resource or may open it to hackers. Virtual directories that cannot be deleted are important to the operation of the device and should be modified only by advanced users and only if necessary.