I am about to take on old Win-XP computer (yes it is that old) to a recycling centre. The computer still runs and of course contains a lot of personal stuff on it as well as old passwords. For example it automatically connected to my home Wi-Fi. What should I do to wipe the disk?
take the hard drive out and melt it with thermite, recycle the rest
Or you could wipe the hard drive using a free program like DBAN before recycling it.
The free programs don’t make it completely unrecoverable but unless you have the NSA digging through the recycling center using all their tech to get your data you’re probably fine. You can change some passwords if you’re really worried.
I sold a couple old computers at a garage sale one time, MINUS the hard drives. Marked them appropriately, of course. There was a guy interested in them who was disturbingly insistent that he wanted to also buy the drives that I removed from them.
I always keep my old HDs for a while, I’ve never figured out why. I have yet to try to pull anything off of them. Anyway, when I run across one I feel like I’ve held on to long enough, I put the claw of a framing hammer through it and chuck it. 28 oz. encryption.
Lots of answers, depending on the age of the computer, what tools you have, and how handy with computer innards you are.
Simplest, brute force - open the computer, unscrew and unplug the hard drive (probably looks something like this. If you’ve got a torx head screwddriver (usually they have that kind of screw), you can take it apart and “destroy” the platters within. You can wipe over the surface with a strong magnet, or take it apart further and physically break the platters.
CAUTION! Those platters are hard, but very brittle - wear protective goggles and gloves!
I’m assuming you have an IDE mechanical hard drive in there, by the way, and that you’re certain you’ve recovered everything off of it. It may be a SATA hard drive, which just has smaller cables.
Alternatively, you can remove the hard drive, and take it to a trusted computer shop (or computer-savvy friend), and ask them to wipe it. It’s easy to do, if you have the tools - say, an external enclosure that handles that particular drive’s interface cables.
Unless this is performance art, I am seconding DBAN. No need to remove anything or take anything apart.
I take the hard drive out and smash it with a 5 lb. hammer. I figure the recycling center can salvage something from it, just not my old files.
True, but the smashing is fun! 
That, and you can recover some wicked strong magnets.
Haven’t used DBAN myself, but here’s a guide from Lifewire.
Third or fourth DBAN. As long as the computer is functioning this is by far the best way to destroy the data on a spinning hard disk (solid state drives require different techniques). Sure, all the physical destruction stuff is fun to talk about, but isn’t really necessary.
This is a bit of a myth, unless you’re talking about wiping old MFM drives from the 80s. Once a modern, and that includes 15 year old, drive has been overwritten, there is nothing to recover. You also have to consider who is attacking you. In this case, it’s the guy who buys the old computer and runs a program to recover deleted files on it. One pass will make that method of recovery completely ineffective. If the government has it out for you, and they don’t get anything from your old computer, they’ll move on to other methods not available to guys shopping for recycled computers.
I just pull the hard drive, whack it a few times with a hammer and throw it in the kitchen trash. The chance that a master hacker will be going through my moldy leftovers and wet paper towels, find the drive, open and physically repair it is low enough that I’m willing to take the risk.
Heat (hot fire) and strong magnetism are two sure fire methods of destroying the drives completely.
‘That old’ bless. I have my Windows 98 and Apple IIe machines upstairs right now 
My preferred method is to use a chop saw to cut them into 1cm wide strips.
I dare the F.B.I. to find my goat porn now!
Sounds like me! I just got a new desktop a few months ago, and I just chucked my old pc into my storage closet off my upstairs balcony. Kept meaning to check out how to make it recyclable, so this is timely for me.
Thanks all!
Sounds fun.
I’d probably do that if I felt like I just had to make sure, but I usually just use one of those programs that writes ones and zeros to it repeatedly.
While something could be recoverable theoretically, the likelihood of anyone spending the kind of cash to do that is essentially nil, especially on some random hard drive they found in a recycling bin or at the Goodwill store.
FWIW- back when I worked in computer forensics, we could recover all sorts of bits and pieces of files that hadn’t been overwritten, but we were pretty much out of luck when it came to files that had been deleted and then overwritten. It took specialized hardware to try and figure out what was under those 1s and 0s that had been written to the drive, and from what I understand even then, it wasn’t a particularly reliable procedure.
I always disassemble the hard drives so I can retrieve the super-magnets inside.
If I ever decide I have enough of those, I’d use a triple-rewrite program as we did when I volunteered at a computer refurbishing nonprofit.
Or hammer it.
Unfortunately, although the internet appears to work and I can search for dban, the connection “resets” every time I actually try to download anything. I guess more drastic measures will be needed.
Can you download DBAN on a different computer? Normally, you run the program by booting from a USB stick or CD-ROM.