In his “Basics” column for The New York Times, Thomas J. Fitzgerald writes that many people who sell or dispose of old computers fail to properly delete confidential data on these machines’ hard drives. Fitzgerald recommends some software programs that will overwrite all old data on a hard drive and make it impossible for others to access the data once the computer changes hands. “If you overwrite it (data) once, it’s gone,” says the CEO of one company that offers disk-overwrite software. (Note: This site requires registration.)