PHYS169@csc.canterbury.ac.nz (Mark Aitchison, U of Canty; Physics) (06/18/91)
BARNOLD@YKTVMH.BITNET writes: > Readers might want to play with an undocumented /MBR switch in DOS 5 > FDISK. It appears to force FDISK to overwrite the code in a PC/PS2 > master boot record, without touching the partition table, and in > limited testing on a half dozen machines it succeeded in cleaning up > machines infected with the Stoned, the Stoned 2, and the Joshi > viruses. This was with the DOS 5 shipped by IBM, not Microsoft's DOS > 5; can somebody please test MS-DOS 5? On a related subject: You may use the DRDOS 5 sys command to rewrite the boot sector (not the MBR, I think), but watch out when you have a diskette infected in such a way that the Bios Parameter Block (that says the disk size, etc) has been junked (e.g. by stoned). The SYS command rewrites a good boot sector around it (fair enough), but acts on the size information in the BPB, and you end up with a disk that needs to be fixed with a disk editor. Remember that DOS normally ignores a lot of the BPB and goes by the ID byte at the start of the FAT; this is because early (version 1) DOS might write anything there. DRDOS reacts sensibly if it contains junk *except* when it comes to the SYS command, so beware. Mark Aitchison, Physics, University of Canterbury, New Zealand.