Quick approaches to prevent users from recovering files from free space

Question

I have an HP EliteBook 8570w laptop with Windows 7 64x, and I am getting a new laptop, so I want to sell my old laptop. I removed all my personal data, but based on my knowledge, users can recover deleted files. So I downloaded a tool named File Shredder, and I chose to shred the free space using the most aggressive approach "Gutmann 35 passes". But since I have 500GB free space, this process is taking too long. Can anyone advise if there is a faster way to shred free space? I thought of this approach: I have an SQL server setup files (size around 2 GB), so if I copy/paste this file multiple times till my laptop's hard disk become full, then I can delete those copies, so in this case I do not think anyone can recover anything. is this correct?

Answer 1

What File Shredder is doing

File Shredder is a utility that you run from within Windows environment. It writes to the same space of the hard drive multiple times, making it harder to recover what was there to begin with.

Methods to "permanently" delete files from Windows

The main ways you can delete files are the following:

1. Delete from your Windows environment - This just removes the files from the file lookup table but can generally be found with File Recovery software pretty easily since the data still exists until it is rewritten.
2. Run zero or random passes to sectors where files were located from within Windows - This is what File Shredder appears to be using. This keeps your Windows OS in tact but targets either an external drive that Windows is not installed to or certain sectors of the Windows one. These type of tools are generally better than the first but can theoretically be found again if Windows stores any information about them.
3. Run zero or random passes to entire hard disk - This method is usually launched from another hard drive, CD, or USB drive as it can't be loaded from Windows since it will also delete windows and everything on the drive. This is the most secure as it basically turns all bits on the hard drive to be 0's (or random bits) as if nothing was there.
4. Destroy the physical drive - Run a drill through the drive or shatter the disc inside then it is pretty much impossible to recover but obviously you can no longer use the drive.

How to decrease the possibility of recovery

Theoretically anything can be recovered but what you are trying to do is make it incredibly difficult / unlikely. Generally you would go with the least expensive approach for what kind of data you are deleting. If you have stuff that isn't top secret then I would recommend free options.

The approach to zero a drive has three important factors:

1. Zeroing / Random algorithm (What's the best algorithm to secure erase HDD?) This is the method the software uses to apply zeroes / random bits. Generally the more expensive methods do a "better" job; however, as pointed out in the link there has not been any published papers or known attackers who could get past a free single pass.
2. Number of passes this is the number of times the software will cycle through the drive writing 0's or random numbers to each bit. The more passes, the less likely it is to recover. Like mentioned in #1 though, nobody published has ever gotten past one pass.
3. Cost Like I mentioned, I would recommend the free methods.

How to go faster?

Your question was how can you make the tool run faster. Based on what I explained above, you can either modify the algorithm / cost or you can modify how many passes the software takes. Since you state that you have it set to 35 passes, I would recommend less passes if you are satisfied with that level of security.