How do you erase data from your hard drive

The theory that your data is still recoverable by forensic analysis by well-financed governments, is based on a misunderstanding of a research paper from the mid 90s by Peter Gutmann, which looked at MFM floppy disks, not modern EPRML hard drives. Lifehacker describes the software that you will be using, Darik's Boot and Nuke, as "an open-source boot disk utility (read: works on nearly any computer) that supports a wide variety of disk wiping methods and operates from inside the computer's RAM, allowing it to scrub the disk thoroughly at a remove.