Author: Only 10 percent of drives I purchased had been properly sanitized. One drive contained financial information from a Boston-area investment firm. Another had e-mail and personal financial records of a 45-year-old fellow in Georgia. Many programs that purport to clean your hard drive so that the information on it cannot be recovered using even the most advanced technical means can be done. All of the programs do the same thing: They overwwrite the blocks on your computer’s hard drive.”]
Source: https://www.csoonline.com/article/2116409/pc-disposal–hard-disk-risk.html