/sys$common/syshlp/helplib.hlb PURGE, Qualifiers, /ERASE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /ERASE
       /NOERASE (default)

    Erases the specified files from the disk so that the purged data
    no longer exists physically on the deallocated disk blocks.

    When you delete a file, the area in which the file was stored is
    returned to the system for future use. The data that was stored
    in that location still exists in the system until new data is
    written over it. When the /ERASE qualifier is specified, the
    storage location is overwritten with a system-specified pattern
    so that the data no longer exists.