Contents
Introduction
The ease and efficiency of using mobile phones, computers, and other electronic devices make our lives easier. We store everything from personal photos to sensitive work documents on these gadgets, often forgetting how valuable the information is until we decide to delete it.
For many people, deleting files seems like an easy task: you highlight the file and press the "delete" button, after which you may believe this file will never bother you again. Nothing could be farther from the truth, though. In fact, most files remain on the storage media until they become overwritten by other data.
Below, this blog goes deep into how file deletion works on every device, the risk it creates against your privacy, and what you can do to make sure deleted files are gone for good.
How File Deletion Works
Before we understand why deleted files are not really gone, let's break down what exactly happens when you delete a file on a digital device.
Mobile Phones
Most modern smartphones use a type of flash memory called NAND flash storage. Whether an Android phone or an iPhone, the type of file system used works in roughly the same way: when a file—a photo or document, say—is deleted, it is not immediately taken completely away from your phone's storage.
The file gets removed from the directory structure of the phone's file system, which is essentially the map that tells the device where your data resides. In such instances, the file remains on the storage medium until the device needs to save new data, at which point it overwrites the old file.
Computers (Windows, macOS, and Linux)
Similar mechanisms are followed in computers. When you try to delete a file on a Windows PC, Mac, or Linux system, the file goes to the recycle bin or trash folder—a temporary holding area provided for recovering files deleted by accident. But even when you empty the trash, the data does not just disappear.
Instead, the operating system simply removes a reference to that file within the file allocation table, which is much like an index at the front of a book where you can look up which page a chapter starts on. The actual data does not get removed from the hard drive—whether HDD or SSD—until it is overwritten by other files sometime later. On older spinning disk hard drives (HDDs), the data could linger for a long period of time. It is a little faster on the now-increasingly-popular SSDs due to how memory is managed, but even then, traces of your data can remain for some time.
External Storage Devices (USB, SD Cards, etc.)
The deletion process works similarly on external storage devices like USB drives and SD cards, just as it does with internal storage in computers and phones. Once a file gets deleted, the space it occupied is marked as reusable, but the actual data stays intact until it gets overwritten.
Why Deleted Files Can Be Recovered
To understand file deletion technically, it's important to realize that deleted files can often be recovered, especially if they haven't been overwritten by new data.
Deleted files can be recovered from mobile phones, computers, and external storage using specific software utilities. These utilities recover files that haven’t been completely overwritten yet by scanning the storage media. Recovery tools can generally recover a file even after the user has emptied the trash or recycle bin, provided it has not been partially or completely overwritten.
For example, in forensic investigations, law enforcement agencies often use advanced data recovery software to recover vital evidence from devices owned by suspects. Similarly, cybercriminals can use the remains of deleted files to recover sensitive personal or financial information for malicious purposes.
SSDs and Data Recovery
While SSDs are generally faster and more efficient than traditional HDDs, their design introduces some complexities when it comes to data recovery. SSDs preemptively erase data to prepare sectors for new data, a process called wear leveling, and send TRIM commands to keep performance high. When the operating system deletes a file, it sends a TRIM command to the SSD that zeros out data in specific blocks, making the recovery of deleted files more difficult.
However, even in the case of SSDs, with some exceptions, information restoration might be possible, especially when the TRIM function is not active or has not been powered on for some time since deletion. Therefore, while SSDs offer slightly more security, users still need to take extra measures to ensure secure file deletion.
Security Risks of Deleted Files
When most users delete files, they assume those files are permanently gone, never to be seen again. As we have seen, this is rarely the case. Deleted files can pose significant risks to both individuals and businesses, especially when sensitive information is involved.
Personal Data Exposure
On a personal level, sensitive information is often stored on phones, computers, or external storage devices. This may include photos of a personal nature, banking information, passwords, or even copies of identity documents. Selling, losing, or otherwise disposing of such a device without properly wiping the data can allow someone else to recover these deleted files and use them for identity theft, blackmail, or other malicious activities.
The increasing use of mobile devices and the internet has raised significant concerns about data security breaches, particularly in countries like India. For example, selling an old smartphone in the second-hand market without properly cleaning it may leave traces of your personal data behind on the device.
Business and Corporate Security
The dangers associated with deleted files are even more serious for businesses. Companies regularly handle proprietary data, financial records, employee information, and customer data. Unless properly erased, such information could fall into the wrong hands, leading to legal, financial, and reputational consequences.
Many industries, including finance, healthcare, and IT, have regulations that require businesses to securely handle and dispose of sensitive data. For example,
in India, the Information Technology Act, 2000 emphasizes data security and prescribes severe penalties for failing to properly dispose of sensitive information.
Methods of Secure File Deletion
Given that deleted files pose a risk, it is clear that the delete button is not sufficient. To ensure that your files are truly gone, here are some methods and tools to help you securely delete files.
Overwriting Files
One of the most common methods of securely deleting files is to overwrite them with random data. Special software tools can overwrite files multiple times, making it virtually impossible for any recovery software to retrieve the original data. This process is also known as data wiping or data shredding.
Several free or paid utilities are available to securely wipe data in both Windows and macOS. Software options like Eraser for Windows or Permanent Eraser for macOS will overwrite your deleted files multiple times to ensure they are completely gone.
Encryption
A powerful way to secure your data is through encryption. With strong encryption in place, even if a hacker recovers a deleted file, they will not have access to the contents without the encryption key. Full-disk encryption options are available for both Android and iOS, encrypting not just specific files but all data on your phone.
For computers, tools like BitLocker in Windows and FileVault in macOS offer system-wide encryption, making it significantly harder for an attacker to recover and decrypt deleted files.
Built-in Tools for Secure Deletion
Modern operating systems often have secure deletion utilities built in. For example, macOS has a Secure Empty Trash option, and Windows has a Cipher utility that securely overwrites free space. Using these tools can give you peace of mind, knowing that your deleted files are no longer recoverable.
Factory Reset
Performing a factory reset is one of the easiest methods to delete files from a mobile device. However, this should be done with caution. Sometimes, simply resetting your phone does not delete everything, and parts of files may remain.
To ensure your phone is completely erased, you should encrypt the phone before resetting it. This added layer of security makes it much harder to recover data from the device.
Physical Destruction
In business environments, physical destruction of storage devices—especially when dealing with highly sensitive data—may be the only guaranteed method of securing the data. This can include activities like shredding hard drives or using special tools that degauss or physically destroy the internal components of a device.
Best Practices for File Deletion
To protect yourself from the risks associated with deleted files, here are some best practices to follow:
- Encrypt Before Deleting: Always encrypt sensitive data using encryption tools. Even if the file remains on the device after deletion, it will be unreadable without the decryption key.
- Use Secure Deletion Software: Use file shredding and wiping utilities to ensure your deleted files cannot be recovered.
- Encrypt Then Factory Reset: On mobile phones, encrypt your device first, then perform a factory reset. This adds a layer of security, making it difficult to recover deleted files.
- Physical Destruction for Highly Sensitive Data: Physically destroy devices that contain highly sensitive data, particularly in business and government environments.
- Regular Data Audits: Periodically audit your digital devices and ensure that sensitive data you no longer need is securely deleted.
FAQ
What happens to files after I delete them?
When you delete a file, it is removed from the directory structure, but the actual data remains on the storage medium until it is overwritten by new data. This is true for mobile phones, computers, and external storage devices.
Can deleted files be recovered?
Yes, deleted files can often be recovered, especially if they haven't been overwritten yet. Recovery tools can sometimes retrieve files even after they have been emptied from the recycle bin or trash folder.
What is the difference between HDDs and SSDs in terms of data recovery?
HDDs generally retain deleted data longer as they do not immediately overwrite the data. SSDs, on the other hand, use TRIM commands and wear leveling, which can make data recovery more difficult but not impossible, especially if TRIM has not been activated.
What methods can be used for secure file deletion?
Secure file deletion methods include overwriting files with random data (data wiping), encryption, using built-in secure deletion tools, performing a factory reset, and physical destruction of the storage device.
How does encryption help with file security?
Encryption transforms data into a format that cannot be read without the decryption key. Even if deleted files are recovered, encryption ensures that the data remains inaccessible without the correct key.
Why is physical destruction sometimes necessary?
Physical destruction of storage devices is necessary when dealing with highly sensitive data that must be securely destroyed. Methods like shredding or degaussing ensure that the data cannot be recovered by any means.
Conclusion
In conclusion, deleted files are rarely truly gone. On a mobile phone, computer, or other external storage device, deleting a file often only hides it from view while it remains stored on the medium until overwritten. Understanding how this works is crucial for protecting your privacy and security, especially in an era where data breaches and identity theft are becoming more common.
By taking proactive measures, such as encrypting data, using secure deletion tools, and physically destroying old storage devices, you can minimize the risks associated with deleted files and ensure your sensitive information is truly gone for good.