You’ve Just Been Erased
Data can be different, talking of whether we wish to keep it, or whether we wish to have it reliably destroyed.
Both can be a challenge; at the moment, let’s talk about destroying data reliably, i.e., preventing it from the possibility of recovery.
That’s not as simple as using delete. What we wish is to be sure no data can be retrieved after file(s) in question are erase reliably.
Important note: we are taking about dealing with personal data. Businesses should follow corresponding regulations, if those do exist, of how data should be disposed of.
Don’t Share Unless Required
Prior to talking about safe deletion, let’s mention an important prerequisite: one should always be sure there are no unreachable copies of the data that should be wiped.
Putting it simply: don’t share data if you ever would need to erase it. Whatever comes to the Net, stays there for good, literally. If there’s even a small chance you would need some file(s) to vanish forever, do not ever post them to public domains. It doesn’t really matter whether the access to the files is restricted or not: if a file can be downloaded by someone but you, you’ve already granted cyberspace type of immortality to this data.
In such case, all you can do is to analyze how to make sure the existence of those data bring you as little trouble as possible.
Now let’s go on with a more optimistic scenario: you have undisputed control over the file and wish the data be removed irrevocably.
Physical Destruction of Storage Device
There are companies utilizing unnecessary storage devices; and if you wish to use their assistance, you should choose very carefully. However, in case if you have particularly important data, third parties are the least desirable part of the process.
One of the most reliable steps to ensure that data will not be recovered, is get your storage device dismantled and disassembled (you’ve got me right – using a screwdriver and other tools of your choice), get inner parts wrapped in coarse cloth, to avoid broken parts flying all around, and hammer them long and strong enough, to turn them into dust.
Note that other means of destruction (incineration, using corrosive agents etc.) are not recommended while at home, since they require special conditions to prevent environmental and/or health hazards.
However, what should you do if you don’t want to destroy the device entirely, but only wish to get data deleted? There are means to do that, as well. Note that those means can be used as additional precaution before destroying device physically.
In short: there’s shred utility supplied by most Unix-like operating systems by default, which can provide military-grade insurance of data erased reliably (overwriting required disk area several times with carefully selected data streams). It’s well-documented; all you need to do is to issue ‘man shred’ command to start. Note: default settings are good enough to destroy the file contents irrevocably, so please be careful when experimenting.
Note that file systems do not always keep file contents at the same physical locations on a storage device. It means you might need to erase unused space on the device in question, prior to shredding it. For better reliability, mount the device in question as an additional file system, create (under root privileges, to use as much space as possible) a file spanning over all the unused space (using ‘dd’ utility) and then shred the newly created file.
Shred can erase the entire storage device. Make sure you have nothing important on it. Once you start shredding the storage device, there are almost no chance to recover anything from it with ease.
In case of Windows, you are welcome to use a freeware Eraser tool. It’s as powerful as the mentioned ‘shred’ and can be used as an alternative to standard deletion. Eraser ensures that the deleted files disappear completely (note: otherwise, there’s good chance that the space use by file is just marked as free, and file contents still can be recovered).
Note that the above is about magnetic storage devices. Erasing memory sticks and sold state drives (SSDs) can be tricky: corresponding means are usually built-in into the device’s on-board controller. If you are a Windows user, you can use Secure Erase utility. Linux users should follow instructions similar to this: Secure Erase under Linux.
A good encryption tool, such as TCNext, can add reliability to data destruction: if only a fragment of data can be recovered, it can make extremely hard to take anything out of it, even if the encryption tool and encryption credentials are known. Thus, keeping all important data within encrypted containers (the best approach is to encrypt the entire storage device) raises chances to delete it reliably.
Note: encryption also required that you ensure you know encryption credentials and ensure physical media works normally, otherwise the same reason can prevent you from accessing your data.
Encryption is also good as a precaution if the storage device is small enough and thus is easier to get stolen or lost accidentally.
Deleting your data can be as tricky as preserving it. However, one or two well-known tools can ensure that your data is safe from being viewed by those not meant to access it.
Note that there can be per-country specific laws regulating the process of data removal (sanitizing), encryption usage and so on. As always, please learn more about the regulations in advance, so as to avoid trouble of a different kind.