Deleting files isn’t enough. Here’s how to properly erase hard drives.

“I have several old computers that I would like to donate to charitable organizations for schools,” one reader wrote in an email. “I have erased the information on the hard drive but have heard that simply deleting data doesn’t remove it completely. Can you advise how to securely wipe data from a computer?”

Unfortunately, they heard right: just because you’ve deleted a file on your computer and emptied the Recycle Bin doesn’t mean it’s gone forever. Making sure those files are properly gone will take some extra work, but if you’re considering donating, selling, or even recycling an old computer with a hard drive in it, it’s absolutely worth putting in the time.

“There are so many stories about people buying used computers online and recovering data,” said Andrés Arrieta, director of consumer privacy engineering at the Electronic Frontier Foundation. “It’s kind of scary. It’s all your life there.”

If you’re serious about keeping your data away from potentially prying eyes, here’s how to securely erase your old hard drives.

For hard drives inside a working computer

If you can actually fire up and use the computer you’re trying to get rid of, consider yourself lucky. With the right software, the process can be mercifully simple. Thankfully, in some cases, the operating system that runs the computer already has everything you’ll need to securely erase the hard drive.

• Click the Settings icon, then click “Change PC Settings”
• Click Update and recovery, followed by “Recovery”
• Under the heading “Remove everything and reinstall Windows,” click “Get started”
• When prompted, select the option “Fully clean the drive”

• Click the Windows button in the bottom-left corner, then the gear-shaped Settings icon
• Click Update & Security, then “Recovery” in the sidebar
• Under “Reset this PC,” click “Get Started,” then “Remove Everything”
• When you get to the “Additional Settings” screen, click “Change settings” and make sure the “Clean data” and “Delete files from all drives” options are enabled

• Click the Windows button in the toolbar, then the gear-shaped Settings icon
• Click on Windows Update. Then click Recovery and select the Reset PC option
• Choose “Remove everything,” and click “Change settings” to make sure the “Clean data” option is enabled

For computers running even older versions of Windows — like Windows XP, Vista, or 7 — you may need to turn elsewhere for the right tools. The EFF also recommends using free apps like BleachBit and DBAN for securely erasing individual files and entire hard drives, respectively.

These can also come in handy if you’re using more recent versions of Windows, too. These apps are well-suited for dealing with especially sensitive data you want gone, or when want more control over the way your hard drive gets wiped and overwritten.

• Turn on (or restart) your Mac, and hold down the Command and R keys while it boots — this will bring your computer into Recovery Mode
• Log into your account (if needed) and click Disk Utility
• Select the hard drive you want to wipe and click the Erase button
• Click Security Options and select how thoroughly you want the drive to be erased. Most people will be fine selecting the second option, which writes over all of your saved data twice

For hard drives inside a nonfunctioning computer

If one of the computers you’re looking to get rid of responsibly doesn’t turn on, it may be better suited for a trip to a recycling facility than to an eBay buyer. But just because the thing won’t boot doesn’t mean the personal data stored on its hard drive is already lost to the ages.

We’re going to have to do something about that. And the first step is gaining access to the hard drive itself.

For folks familiar with the inside of a computer — or anyone eager to poke around in there — one approach is to crack the PC open and grab that hard drive. Don’t worry: often enough, this is much easier than it sounds.

Most desktop computers can be opened quickly, and assuming there aren’t a bunch of parts in the way, disconnecting the hard drive shouldn’t involve much more than unplugging some cables and removing a bracket. This process can be trickier for laptops, so it’s a good idea to search for a repair guide or a YouTube tutorial for your specific model before taking the plunge.

Once you’ve managed to free that hard drive from its metal prison, use a USB drive enclosure or docking station to physically connect it to another computer, where you can use the software tools mentioned earlier to responsibly erase them.

If this sounds like a pain, there’s always the easy way: you could take your machine to a local repair shop where they could pop out that hard drive in mere moments. (For all its quirks, Yelp is a helpful place to start looking for these shops.) They could probably also securely wipe it for you too, which would save you even more time.

The Office Space approach

There’s also the low tech — and some might say more therapeutic — approach. If you can physically remove your old hard drive from a computer you’re planning to recycle anyway, take the drive outside and apply a liberal dose of sledgehammer to it. A rock from your garden would work too, as would using a drill to make four or five big holes around the center of the hard drive.

Really, go with whatever feels right when the name of the game is doing some Office Space-style damage. (Just don’t forget the safety glasses.)

“If you were just going to throw it in the trash anyway, sure, hammer it,” Arrieta said. “Why not have fun with it?”

Specifically, what we’re trying to do here is foul up the drive’s platters, the spinning discs that our data is meticulously, magnetically placed upon. Destroying these platters won’t always make your data completely irretrievable, but it makes the process of salvaging any of that info more trouble than it’s worth in all but the most extreme cases. (If you’re holding onto, say, government secrets for example, you’re probably better off shredding the drive entirely.)

Once you’ve had your fun, though, don’t just toss that busted drive in the trash — find a local e-waste facility and drop off its carcass there.