If you want to make sure the file is safe from prying eyes, you must shred it, namely write zeros over top of all the data before deleting it. However, even that won’t stop the spooks from retrieving it with sophisticated hardware. The DoD recommends wiping several times, with the bit complement and with random data. But even that won’t stop the big budget spooks. The Navy chops up old hard disks rather than wiping them to keep the data safe, so obviously the DoD recommendation will allow the DoD to read your disks if they chose.
However if the file has already be deleted, you need to wipe the free space between files, by overwriting with various patterns.
Files are allocated space in even numbers of clusters (usually 4K). So there is some unused space at the end of the file, that can contain embarrassing data. Wiping can delete these cluster tips aka file tails too.
Another reason to wipe is to help compress image backups. If you wipe all the free space, all the unused space at the end of each file, and all the unused directory slots to zeros, then the compression algorithm will be able to compress this unused space to almost nothing. Wiping to a random value won’t help since the compression algorithm will treat it as valuable complex data.
The 12 Ghosts Shredder program handles all your wiping needs and costs only . It is the most popular wipe download from Tucows. However I would go so far as to call it a Trojan. I do not recommend using it. First the nagware is unbelievably rude and annoying. It interrupts you ever few seconds even in the middle of an operation. It sometimes opens your editor and displays the copyright screen. It just does not make sense to so majorly hassle people for just a buck. It is like a stickup man holding people up and demanding only a dollar.
To add insult to injury it left tens of dozens of delete-me icons all over the desktop, menu, task bar etc.. When you go to delete them, if your hand is not rock steady, in typical Vista fashion, they duplicate, after the manner of Perseus killing the mythical Greek Hydra. It addition in placed tens of thousands of delete-me 0-length files in every directory on my drive. I had to write a computer program to get rid of them all.
I use Ace Utilities to do my wiping. It has every feature I want. You have to go into options to configure a pattern of wiping with a single pass wipe to 0 though. You can make up your own wiping pass patterns.
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