How to erase data so no one can recover

When you a delete a file, it isn’t really erased – it continues existing on your hard drive, even after you empty it from the Recycle Bin. This allows you (and other people) to recover files you’ve deleted.If you’re not careful, this will also allow other people to recover your confidential files, even if you think you’ve deleted them.

What Happens When You Delete a File
Windows (and other operating systems) keep track of where files are on a hard drive through “pointers.” Each file and folder on your hard disk has a pointer that tells Windows where the file’s data begins and ends.When you delete a file, Windows removes the pointer and marks the sectors as free. but that file is still recoverable by data recovery tools.

Why Deleted Files Aren’t Erased Immediately
If you’re wondering why your computer doesn’t just erase files when you delete them, it’s actually pretty simple. Deleting a file’s pointer and marking its space as available is an extremely fast operation. In contrast, actually erasing a file by overwriting its data takes significantly longer. For example, if you’re deleting a 10 GB file, that would be near-instantaneous. To actually erase the file’s contents, it may take several minutes – just as long as if you were writing 10 gigabytes of data to your hard drive.

Preventing Deleted Files From Being Recovered
You can use a utility that automatically wipes your hard drive’s free space – by writing other data over the free space on your hard drive, all deleted files will be erased.
For example, CCleaner’s integrated Drive Wiper tool can do this.

To make sure that a single file can’t be recovered, you can use a “file-shredding” application such as Eraser to delete it. When a file is shredded or erased, not only is it deleted, but its data is overwritten entirely, preventing other people from recovering it.

To really prevent someone from recovering any of your data, you can use a disk-wiping program, such as DBAN (Darik’s Boot and Nuke.) Burn DBAN to a CD, boot from it, and it will erase everything from your hard drive, including your operating system and all your personal files, overwriting them with useless data. This is very useful when getting rid of a computer — it helps you ensure all your personal data is erased.