Most Windows users know that when you delete a file it isn’t really deleted. In the first instance it is stored in the Recycle Bin, which gives you a reprieve on those occasions when you didn’t mean to delete it in the first place.

If you empty the Recycle Bin, the files are ‘deallocated’ from your hard drive. Again, the files aren’t deleted: the space they occupy is merely marked as available to use.

This is the reason why undelete utilities work: you can get back deleted photos and files without too much hassle if you act quickly.

But what about those times when you want to ensure no-one can recover a particular file? That’s when secure deletion utilities come into play.

How do I permanently delete a file?

Not many people know this, but Windows has its own built-in secure deletion tool called Cipher that's been present since Windows XP came out. If you prefer not to download any third-party software, this is going to be the best method for you. And while we're using Windows 10 here, it works on all versions back to XP.

Cipher doesn’t have a graphical interface so it isn’t amazingly user friendly, but the command you need to type is simple enough.

NOTE: You must delete the files you want to securely erase before running Cipher. This means emptying the Recycle Bin, or selecting the files and pressing Shift+Delete. Cipher only securely erases files which have already been deleted.

To run Cipher, launch PowerShell (which has replaced Command Prompt) by right-clicking on the Start menu and choosing Windows PowerShell from the menu.

Now type the following:

cipher /w:C:

What this will do is to securely overwrite all the data on the C: drive which has been deallocated. In other words, it won’t touch any data which has not been deleted, so it will not delete everything from your C: drive. It only deals with the files which have been deleted.

How to securely delete files in Windows 10

This can take a very long time, so if you want to speed things up, you can specify the exact folder where you want ciper to operate by typing the full path.

For example, if you wanted to securely erase everything which has already been deleted in your Documents folder, you need type in its location as follows:

Cipher /w:C:\Users\Jim\Documents

Obviously, replace Jim with your username. If you don’t know what that is, then open a File Explorer window (Win+E is the shortcut) and click on:

This PC > Local Disk (C:) > Users

There you will find a list of the user accounts: it should be obvious which is yours.

How to delete files securely with Eraser

If cipher isn’t for you, then there are a number of free utilities which will do a similar job of overwriting your deleted files to make them unrecoverable.

We recommend using Eraser, which is a completely free, open source utility which you can download via the Heidi website.

Click Download in the top menu, then on the latest version (usually at the top of the list). This will redirect you to a download mirror – a different website – where the file should automatically begin downloading.

If you choose the Typical option when prompted during installation, Eraser will add itself to the right-click menu. This means you can select one or more files in File Explorer, right-click on them and choose Eraser. That’s the easiest way to use it.

If you launch the application itself, you must right-click in the Erase Schedule space, click New Task > Add Data. Then you can choose what to delete: files, folders, unused disk space, Recycle Bin and more.

How to securely delete files in Windows 10

You can name and save these tasks and run them on a schedule. There’s even the option to choosing some innocuous files to use to overwrite your deleted files to ‘allow plausible deniability’.

If you don’t do this, someone looking at the contents of the drive would see the tell-tale patterns of a secure deletion and realise that you didn’t want certain files to be found. They wouldn’t be able to recover them, but if you overwrite your sensitive data with other files, it hides the fact they’ve been deleted.

To free up more disk space, here's how to delete duplicate files.