Destroying files

[Charles G Waldman]

Darrell writes:
 > >Randall Hopper
 > > Safest bet is a reformat of your hard drive.
 > 
 > I think reformatting only destroys the linkage between blocks. The data
 > remains.
 > 
 > Write in 'C' for DOS something that will write to a file until the disk is
 > full. Boot into DOS from floppy delete everything and run your disk filler.
 > And reformat for good measure.
 > 
 > Repeat until paranoid concerns are diminished to acceptable levels.

If you're really paranoid, you will worry about "bad blocks" - data
could be written to the disk into a block which is subesquently marked
"bad" by the disk controller; after this even "write zeros to the disk
until it's full" won't overwrite information in "bad" blocks.  A
sufficiently determined "bad guy" with the right tools could possibly
get at this information.

I've read that the military actually grinds up old disk drives, and
that some people even worry that since bit-densities are so high on
current-day disks that even after "grinding" one of the fragments
might contain recoverable data.  Seems unlikely to me, but I've read
that people in the military worry about this.