Let’s stick some more with Windows tools. A few years ago it became hip to wow friends and family with tools that would undelete or recover files long through gone from hard disks. This led to the eventual realization that old computers given away and drives lost or stolen could yield a lot of data if not properly wiped. If you ask me, if there is any doubt about a whether a drive’s contents are sensitive or not, just destroy the drive when it is decommission. (Besides, the powerful magnets inside the drives when disassembled make for fun toys for most anyone, if you want to score some points.)
You can use Eraser as a tool to better wipe files from a Windows system. Use it in conjunction with the recovery tools above to see the differences. For full disk wipes, I prefer the bootable DBAN disc.
Of course there are more tools! Here’s a quick list I pulled from a mailing list:
another Secure Delete
and of course, shred for Linux, which should need no link.