Recovery: corrupt oracle block for test

C:\oracle\product\10.2.0\db_1\database>vim test.null
insert : 0
C:\oracle\product\10.2.0\db_1\database>dd if=test.null of=C:\PROJECT\TEST10G\DATAFILE\O1_MF_TEST_UND_6MBTLQRW_.DBF bs=8192 seek=3 count=1
0+1 records in
0+1 records out