It’s a common misconception that once having deleted your documents from your computer they are gone for good. Wrong. It doesn’t matter if you empty your trash bin or recycling bin, your old files may still be within a moment’s access. This is especially important when you are ready to sell your old laptop or desktop. Formatting the drive won’t be enough either. Many user friendly recovery tools exist that allow potential attackers easy access to your deleted personal data.
Data on a Hard Disk Drive is never erased, only written over. To effectively erase data, you will need to write over it. But why is this not done by default? Efficiency.
Rather than spend time and resources writing over every file you delete, your system simply marks the space as available to use. Eventually over time another file will likely write over this available space, making the old data for the most part irretrievable. The problem is, because files are written fairly randomly over your drive, it is difficult to know if and when this will happen.
Solid State Drives tend to be a bit more secure in this respect due to the trim command. When files are deleted on an SSD, the built in trim command marks the sectors as no longer containing valid data. Usually once this happens, the data in question is irrecoverable. The problem is that many drives implement trim differently. This means that once you delete a file, you may not know how long it will be until that data is effectively wiped.
How to wipe?
As mentioned, data on a HDD is only written over, never erased. There are many programs you can find to do this. My personal choice has always been Darik’s Boot and Nuke (DBAN). DBAN, as well as many other software erasure solutions have their limitations.
You will find that often you will not be able to wipe the HPA, DCO or bad sectors of a hard disk. This, for most users, is not an issue as these are not areas of the HDD where you would keep personal information. Generally these tools will offer to rewrite your entire HDD multiple times. For most users, one wipe is enough. After this point, it is unlikely that any data will be recovered without highly specialized equipment.
SSD drives will not be effectively wiped by most software solutions. Because of complex algorithms SSD drives write to the drive in a way that will avoid wear. This means that software may leave much data untouched. You will end up putting additional wear on the drive, without wiping your drive as intended.
Instead you will likely want to use the “ATA erasure” command. This applies a voltage spike to the NAND memory on the SSD drive, effectively flushing all existing data in an instant. You can search online to learn how to use this command. Take caution when using the “ATA erasure” command as it is not very well tested. The risk of destroying your drive does exists.
What about the cloud?
You are likely out of luck in this case. Once you pass your data onto a cloud service, not only are you agreeing to the company’s terms and conditions, but also to whatever laws govern the countries the data travels through. You are also at the whim of the company’s security policy’s. This can be good or bad, the point is that it is out of your hands. If you are not able to have your own “private” cloud, do your research. Try to find a company you are willing to trust. When loading your data onto a cloud service, do so with the understanding of what that means for your data.
Before you get rid of your old computer, wipe it! It doesn’t matter if you are giving it to friends or family, you never know where that laptop might end up in the distant future.