In light of the fact that many web sites (such as USENIX) have not updated Prof. Gutmann's paper to include his Epilogue; especially the sites promoting a 35-pass program FOR SALE, I decided to include his comments here. This is a verbatim copy from the end of his paper (which can be found at: http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html ). ========================================================================== Epilogue In the time since this paper was published, some people have treated the 35-pass overwrite technique described in it more as a kind of voodoo incantation to banish evil spirits than the result of a technical analysis of drive encoding techniques. As a result, they advocate applying the voodoo to PRML and EPRML drives even though it will have no more effect than a simple scrubbing with random data. In fact performing the full 35-pass overwrite is pointless for any drive since it targets a blend of scenarios involving all types of (normally-used) encoding technology, which covers everything back to 30+-year-old MFM methods (if you don't understand that statement, re-read the paper). If you're using a drive which uses encoding technology X, you only need to perform the passes specific to X, and you never need to perform all 35 passes. For any modern PRML/EPRML drive, a few passes of random scrubbing is the best you can do. As the paper says, "A good scrubbing with random data will do about as well as can be expected". This was true in 1996, and is still true now. Peter Gutmann. (Some time after July, 1996 and before February 2002; no date is given in the paper for this Epilogue.) =========================================================================== EOF.