How to permanently delete files from your PC, mobile devices
If you are familiar with computer technology, you must know that delete a file from the hard drive will not actually delete a file. Once you run delete command or empty the recycle bin, the computer actually removes the index to the file but keep the file in the memory. It means the user does not have access to the file, although the file still sits somewhere in memory. If you want to recover that file, there is plenty of software available in the market you can use to resort deleted files.
There is some process you have to follow to actually delete the file permanently. We will discuss some scenarios where you might want to delete your files permanently. If you are a PC user you might want to delete the file from your personal computer because you are selling the computer or hard drive to someone else. You might want to delete all your data from cloud because you want to close your account.
How to completely clean the hard drive
Before disposing of your hard drive or selling your computer to someone you don't know, it is a good idea to completely wipe out your personal data from the hard drive. Usually people just run format command and think that they have removed everything from the hard drive. But this is not true always. By default format command only removes the index value of the file on your hard drive and your file is still sitting in a hard drive. To securely remove all the files from your computer, you have to write complex commands and follow special algorithms.
To make your task easier, there are applications in the market which could help removing all your files completely. One of the free applications that provide secure erase is Darik's Boot and Nuke (DBAN). This application is designed for individual users. According to the creators of the DBAN, this software takes all known methods of forensic analysis into account, although it does not guarantee hundred percent data removal.
DBAN can be copied to a USB drive, "burned" CD-R or DVD-R (image size is around 11 MB) and is used as the boot disk. You do not have to worry about any operating system you are using just copy the software on a USB and boot it from there.
Completely remove the "deleted" files
However, there is always a need to clear the entire hard drive, more often you just need to get rid of the individual files. You can use the Eraser which is free windows application works with all versions of Windows starting with XP. As stated in the description, the Eraser used Gutmann algorithms designed to effectively remove the content from the hard drive. The software only works with drives under Windows and repeatedly overwrite all deleted files and folders to pseudo-random data based on different algorithms.
Remove protected or locked files
It is not uncommon to find files that can not be removed even using normal deletion method. The best way to identify these files is, you receive an error message stating that the file cannot be deleted. This could happen for various reasons: block access to the file system, running program, restrictions on access for particular user, drive is fully protected etc.
To be able to delete your own files, you can install a free utility called Unlocker for Windows operating systems, it works for both 32-bit and 64-bit versions. Unlocker integrates into the Windows interface and is accessible by right clicking on a locked file or folder.
Remove files from external drive
To fully remove the files from an external drive (such as a USB drive), you can use the CCleaner which is developed by Drive Wiper. It comes for windows and OS X users. Download the application on your computer, install it and choose the option to erase the disk, choose the drive and the appropriate method of erasing data.
Remove files from portable devices
To securely remove pictures and videos from the camera's Flash card, just connect the camera to the PC and you can use the eraser to securely delete files. Most cameras have the option to format the card completely, you format the card using the camera application itself and it is 100% secure.
Deleting files in smart phones and tablets usually is not a problem, The only thing you should remember are the copy of files that are displaced during synchronization to a computer"cloud" services, like Picasa and cloud. If you do not want to sync your pictures in the cloud you can turn off this option in the settings.
Remove files from Dropbox
Dropbox is a Popular file sharing service, Dropbox saves deleted files for 30 days in case you change your mind and want them back. However, if you firmly decided to get rid of specific files, you need to enter the site and click on the Dropbox bin icon on the top right labeled "show deleted files" and remove them permanently.