Database Block Corruption Type = Unknown

I have an Oracle Enterprise Edition database version 10.2.0.5.0

We are reporting: CORRUPTION_TYPE = UNKNOWN in the v$database_block_corruption table.

I am having trouble finding a definition for 'UNKNOWN' corruption. 

SQL> select * from v$database_block_corruption;

     FILE#     BLOCK#     BLOCKS CORRUPTION_CHANGE# CORRUPTIO

---------- ---------- ---------- ------------------ ---------

        10     402955         51         2.4586E+10 UNKNOWN

        10     527595          4         2.4586E+10 UNKNOWN

        11     219553         24         2.4586E+10 UNKNOWN

Need your help in defining 'UNKNOWN' block corruption as well as resolution steps.

Thanks!