Secure Delete – Do You Need It?
Secure Delete makes sure that when you delete a file it can’t be recovered. Understanding Secure Delete is important to protect your data properly. Depending on your level of healthy paranoia and the sensitivity of your data, plain old “delete” may not always be enough.
Deleting a file in Windows doesn’t actually erase the data. In fact, it doesn’t really even delete the file – in Windows Explorer if you delete a file, it’s just moved to the recycle bin. It will only be deleted when the recycle bin gets full or you empty it yourself. However, even a “permanent” delete bypassing the recycle bin doesn’t really erase the data. In a sense, 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 remains in place.
A good example might be moving out of an apartment, but leaving your stuff inside. Until your stuff is replaced by someone else’s, it’s still there and available to anyone who knows how to access it.
Secure delete overwrites the data in the file when the file is deleted. While this takes longer because the entire file must be accessed, it ensures that the data is no longer available to the casual observer. It would be like moving you and your stuff out of the apartment, making sure to leave it empty.
While it might seem that overwriting one file with another would do this, unfortunately it does not. The problem is that you don’t control where Windows is going to write the data. It may 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 very common technique.) The normal “delete” that it does in this case is still not a secure delete because the data is still out on the hard drive.
If this concerns you, then you probably need a secure delete utility. It ensures that the actual locations on the hard disk which your file occupied will be overwritten with other data. On free utility for this is SDelete, available from Microsoft. It can also erase the data from any and all files that have already been “permanently” deleted.
One more thing to look at – again depending on your level of paranoia and the sensitivity of the data – is recovering data that has been overwritten. Because of the way hard disk magnetic material works, it might be possible to actually recover data that has been overwritten. It requires special tools and techniques (plus often a fair amount of money), but it sometimes can be done.
The solution is to ensure that your secure delete utility has an option to overwrite the data multiple times. By writing over those soon-to-be-free sectors multiple times, the original data is irretrievably gone.