How does one sell a computer safely?

[Count Dooku]

Are we talking about the absolute remote possibility of someone taking out the HDD's disk and using god-knows-what kind of tracking based on the immensely faint magnetic imprints left over on the disk after thousands of rewritings?
How many such machines even EXIST? And why are we worrying about something like this happening to someone who just wants to sell his old computer?

Look, they're on to me. The must know I've been in contact with the dark lord of the sith, and they want to know what my plans are regarding the trade federation.

I am a scientist, but I don't use a computer for anything (it's all in a lab notebook, and if anything is useful, it's going in a journal anyway).

If things are looking up financially, I'm going to buy a 32 gig hard drive or something and stick it in one of the computers I sell, and I'm going to keep the largest hard drive for myself on the computer we're keeping. There isn't any reason to do away with so much extra space, and I do think that it would be harder to sell a computer without a hard drive. The other computer will be run with dban and sold. From what I gather here, your average person won't be able to get any meaningful information from it, and if they do, the chance that it will be my SSN, drivers licence number, or banking information is next to nil.

On another note, my CPU (AMD x2 3800+) is for some reason running constantly at 65% or more. I just ran CCleaner yesterday, and I fear my computer is infected with some form of malware. Norton did block something called "blah trojan horse rule" last night, but presumably that means said trojan horse didn't get on to my computer. My preferred tool is adaware. Is this enough?

[RThurmont]

A simple and effective way of eliminating data from an HD prior to resale isn't to zero it out, but rather, overwrite it with random data.

If you boot up a Linux live cd, you can just run this command:

dd if=/dev/urandom of=/dev/sda

Doing that will copy the contents of the kernel's psuedo random number generator to the disk. Just letting that run for a few hours should fully nuke everything, or at least enough of everything so that, from a consumer standpoint, the unit is safe to sell.

Identity thieves are after easy targets, and do not typically have the multimillion dollar budgets to be able to do sophisticated hard disk recovery of disks that have even been zeroed out, let alone overwritten with randomness.

Governments do destroy disks, but that's only because there are a number of extremely well funded intelligence agencies out there with budgets in the ten figure range who would love nothing more than to be able to recover data from discarded HDs. At that, its probably overkill in a large number of cases, given the number of leaks that occur, and that are widely publicized in the national media, involving government employees.

If you really wanted to be sure an HD was gone, pulverize the platters and scatter the powder into the oceans.