How to stop hackers from reaching your deleted files

How to deal with a lost, stolen or retired phone or mobile device

Picture: Levent Ali, Flickr

Picture: Levent Ali, Flickr

What happens when you delete a file? Unknown to most, deleted data from a mobile phone can still be shared with others if not appropriately managed. In a worst-case scenario, this could end up in the hands of a hacker or e-criminal, and used against you.

With most IT equipment, when a file is deleted, one of two processes could take place: logical deletion or physical deletion. Logical deletion, where the file system space the file occupies is marked as available, is used by almost all operating systems for performance reasons, but at the cost of keeping the information physically stored until it happens to be overwritten with the contents of a new file. In contrast, physical deletion modifies the data of the deleted file bit by bit, by creating junk content on the storage medium. This ensures the data cannot be recovered, but takes much longer and therefore usually is considered undesirable for tasks where the user experience is central.

Ultimately, even after you delete a file, there is a chance your information can be recovered.

What happens if you restore to factory settings?

This can vary depending on the platform. Research carried out in early 2015 revealed performing a factory reset on Apple and BlackBerry devices prevents information from being later recovered, due to the physical deletion procedure as well as a stronger control over the companies' hardware.

However, encryption is not included by default on all Android devices, consequently making it possible to recover a lot of the data that had been stored on them, even after running several factory resets.

What are the dangers of logical deletion?

As personal devices and cell phones hold an array of totally private data, from credit card details, web browser history and passwords to more personal information such as contact details of friends and family, photos, texts and access to social media accounts.

Naturally, access to such data could enable a cybercriminal to orchestrate a social engineering attack against the handset's owner leading to extortion or fraud.

For this reason, taking preventive measures up-front are vital to minimising risk of data theft or misconduct.

So, how can you protect yourself?

Read more: ​Sony Xperia X Performance review: Sony’s most disappointing product in years

Luckily, there are numerous precautions you can take to ensure you don’t fall victim to identity fraud or other cybercrimes:

- Encrypt the device

This is the simplest option for Android users. When activated before restoring the factory settings, encryption makes the data unable to be deciphered even if the data is not physically deleted. Remember, the more complex the password, the more difficult it will be for cybercriminals to crack.

You can encrypt your Android system by going to Settings > Security > Encrypt device, and the reset options are located in Settings > Backup & reset > Factory data reset. Also, note that if extra storage, such as a micro SD card, has been installed in devices that support it, you need to decide whether you wish to encrypt that also. These are typically referred to as “external SD cards”, and encrypting them requires an additional step. Another way to format the device’s storage is by accessing recovery mode. However, the results of this method are the same.

Read more: Review: Incipio OtterBox and 3Sixt cases for the Samsung Galaxy S7 and S7 Edge

- Reset the device

Although some apps on the Google Play Store promise to overwrite certain parts of the device storage that have been marked as free by the operating system, that free space may still contain the original data. A factory reset needs to be carried out both before and after running the app. In addition, users will need to avoid using the Google Play Store to install the app, so as to avoid entering their Google account data into the phone again.

- Remove all external cards

If a phone is sold or given away, don’t forget to remove the SIM card and also the micro SD card.

Mobile privacy is a growing concern and with the rise of data breaches, costing a whopping A$2.82m on average for enterprises in Australia, it’s important for consumers to be privacy savvy and take on a proactive approach to protecting personal information. Understanding best practices is the first step, but taking this information on-board and embedding it into your every day lives and habits are imperative.

Nick FitzGerald is Senior Research Fellow at ESET

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