What really happens when you delete a file (and how to wipe a laptop before you sell it)

You press Delete, empty the Recycle Bin, and the file is gone. Except it usually is not. One small fact about how computers work explains a lot of avoidable embarrassment when old devices change hands.

What deleting actually does

When you delete a file, the computer rarely erases its contents. It removes the file's entry from the directory and marks that space as available. The data sits there until something new happens to be written over it, which could be minutes or years later. Recovery tools simply read the space the computer was told to ignore.

Why phones and modern drives are only partly different

Many modern drives and phones clear freed space faster than old hard disks did, and most current phones encrypt their storage by default. That helps, but you should not rely on luck. If a device holds banking details, ID photos or client files, treat it as sensitive until you have properly wiped it.

How to wipe a Windows laptop properly

• Back up what you want to keep, and sign out of accounts and paid software.
• Open Settings, System, Recovery, Reset this PC and choose Remove everything.
• Look for Change settings and switch on Clean data (the exact wording can vary by Windows version). It takes longer, and that is the point.

Phones

On an iPhone, sign out of your Apple account first, then use Settings, General, Transfer or Reset iPhone, Erase All Content and Settings. On Android, remove your Google account, then run a factory reset. Take out the SIM card and any memory card before the phone leaves your hands.

If a device held something truly sensitive and you cannot wipe it with confidence, keep it, or have it destroyed. A few thousand naira of resale value is not worth a leaked identity.