Whether you are in need for quick money and want to sell your computer or simply feeling generous and giving your old PC to your younger brother, you would certainly like the future owner not to access your sensitive data. The problem is that even if you deleted all your personal files from the HDD, the stakes are high that data can still be recovered. How to solve this problem?
First of all, if you have an SSD drive with TRIM mode enabled you don't have to worry - once you have deleted something from your hard drive it is removed forever. But if you use an old-fashioned hard drive you may have to employ additional tools if you want to make sure your sensitive data is no longer accessible after removal.
Shouldn't re-installing the system or using "Reset a PC" tool (in Windows 8) get rid of the problem? Actually, no. In case of HDDs, the system does not remove your data from the disk immediately, but rather leaves a mark in that sector saying that it can be used in the future.
Therefore when you want to remain 100% safe and sound you should use a wiping tool. Such a program overwrites the marked areas on your hard drive, placing some information (usually a bunch of nonsense) so the data that was there earlier can no longer be accessed. Without such a wipe people could recover you sensitive files with an application such as Recuva.
You can deal with your data in two ways, depending on whether you have Windows 8 or not.
#1 - Reset your PC, than wipe your files (on Windows 8)
To reset your files first, use a Reset your PC feature that Windows 8 is equipped with. Once you have done it, you should obtain a clean disk without any additional data (or so it seems at the first glance). You can also do a reset on your non-Windows 8 phone by using the recovery partition or simply re-installing your system from a CD.
Download and install CCleaner and use the Driver Wiper tool to wipe all the sensitive data that has lived through the process of resetting or re-installing your system. This way you will know that no data can be recovered later.
#2 - Wipe your hard drive, then re-install the system
If you would rather wipe your system first and then re-install the operating system, you can use DBAN (Darik's Boot and Nuke), a tool that allows you to get rid of anything on your hard drive - your Windows included.
After the nuking process you can re-install the system from an installation or recovery disc. Remember, however, that since the recovery partition on your hard drive will be wiped completely as well, you will not be able to get the system back from it.