Q: I’m donating my old PC to charity. How can I wipe off all my old data, including any credit card numbers, tax information and household budgets?

A: Deleting everything on your hard drive, or reformatting your hard drive doesn’t truly eliminate its information. Many data recovery specialists can still recover the files, a fact handy to know if you’ve accidentally wiped out your entire hard drive.

To really erase your information, you need to write new information on top of it. In today’s world of exponentially increasing identify theft, many free programs on the Internet offer to overwrite your data with zeros or random numbers.

Some programs overwrite it many times, truly smashing the data. The Department of Defense 5220.22-M specifications call for data to be overwritten three times with different characters each time. The best data killers write over your data seven times, but that’s probably overkill unless you’re James Bond.

The free program Darik’s Boot and Nuke (DBAN) does a fantastic job of detecting hard drives from a wide variety of manufacturers, and then scrubbing them completely clean of data. DBAN works by creating either a bootable floppy, CD or DVD that you place in your PC’s disk drive. When you restart your PC, it loads from the disk, not the hard drive, letting DBAN do its work. It renders your data useless, both to you and the vast majority of data recovery specialists.

Once you wipe the drive clean, reinstall your copy of Windows, place your original Windows CD into the box with your PC, and ship them both to a charity, knowing your TurboTax files won’t fall into the hands of strangers.

(The above information is taken from my book, PCs: The Missing Manual.)