Secure Delete ensures that when you delete a file, it cannot be recovered. Understanding Secure Delete is important to properly protect your data. Depending on your level of healthy paranoia and the sensitivity of your data, the old “deletion” may not always be enough.
Deleting a file in Windows doesn’t actually erase the data. In fact, the file isn’t even deleted – if you delete a file in Windows Explorer, it just moves it to the trash. It is not deleted until the trash can fills up or you empty it yourself. But even a “permanent” deletion that bypasses the recycle bin does not actually delete the data. In a way, it just tells Windows that the disk space where there used to be a file can now be used for something else. Until overwritten, the old data will remain in place.
A good example might be moving out of an apartment, but letting your stuff in. Until your stuff is replaced with someone else’s, it’s still there and available to anyone who has access to it.
Safe delete overwrites the data in the file when the file is deleted. While this takes longer because the entire file has to be opened, it makes the data no longer available to the casual observer. It would be like taking you and your things out of the apartment and leaving them empty.
While it may seem like overwriting one file with another would do this, unfortunately this is not the case. The problem is, you don’t control where Windows will write the data. It can copy the data to a new file on the hard disk and only then delete your old file and then rename the new file to the old file. (A common technique.) The normal “deletion” it does in this case is still not a safe deletion because the data is still on the hard drive.
If you are concerned about this, you probably need a safe uninstaller. It ensures that the actual locations on the hard drive that your file occupies is overwritten with other data. A free utility for this is SDelete, available from Microsoft. It can also erase the data of any files that have already been “permanently” deleted.
Another thing to watch – again depending on your level of paranoia and the sensitivity of the data – is recovering overwritten data. Due to the way the hard drive’s magnetic material works, it may be possible to actually recover overwritten data. It requires special tools and techniques (plus often a fair amount of money), but it can sometimes be done.
The solution is to make sure that your Safe Removal Tool has an option to overwrite the data multiple times. By writing multiple times on those sectors that will soon be free, the original data has disappeared irretrievably.