Craig Ball tells it how it is:

Ambling along the back roads of listservs and blogs, I often come upon a flea-bitten claim that, "Top notch computer forensic examiners have special tools and techniques enabling them to recover overwritten data from a wiped hard drive so long as the drive was wiped less than 3 or 7 or 35 times."


You only need one complete pass to eviscerate the data (unless your work requires slavish compliance with obsolete parts of Department of Defense Directive 5220.22-M and you make two more passes for good measure).

No tool and no technique extant today can recover overwritten data on 21st century hard drives. Nada. Zip. Zilch.

Hopefully he’ll do similar column on encryption which, despite what you see on television, is safe and effective so long as you stick to the public algorithms (like AES, Serpent, Twofish, or Blowfish) implemented in an open-source platform like TrueCrypt. Everything else (i.e., closed or proprietary systems) should be presumed snake oil.

Fact is, data breaches generally occur not through esoteric means like unwiping drives or breaking encryption, but through ordinary oversights like human breach (inadvertant or intentional) or failure to delete properly (like the failure to wipe a hard drive, or failure to wipe backups and copies retained by other users).