Windows – Securely erasing all data from a hard drive

I am about to sell my old desktop PC and I am cautious about some of my sensitive information being available to the purchaser, even after reformatting the hard-drive, using data recovery software.

How can I securely wipe the hard drive so that the data on it cannot be recovered?

Although I specifically want help with my Windows PC, it wouldn’t hurt if there were suggestions for Macs as well.

Solution:

Look into Darik’s Boot and Nuke. It’s a bootable CD which lets you securely erase your hard drives.