Q. I want to donate my computer to charity, and heard I should first remove the hard drive. I don’t know to do that. Is there an easier way?

A. The problem you’re facing is that computer files aren’t really removed when you hit the delete key or empty your Windows recycle bin or Macintosh trash basket. Rather, those actions simply tell your computer’s operating system that part of a disk or drive is available to be overwritten with new data, as happens when you do such things as save files or install software.

Until that overwriting occurs, the old data remains and can be retrieved by savvy techies—including identity thieves who buy old computers in hopes of finding personal information.

However, to stay safe, there’s no need to tear your computer apart and remove your hard drive. You can find free programs that permanently remove files from PCs at FileShredder, KillDisk, and Darik’s Boot and Nuke. Other PC programs are available, usually for about $50, at computer stores and on the Internet.

Mac users have an easier time: Most of those computers come with data-wiping tools built into their systems, so to securely delete a folder or file, move it to the trash can and from the Finder menu select “Secure Empty Trash.” Alternatively, the Disk Utility program “Erase Free Space” scans your hard drive for unused space and securely deletes it. This program is found in the utilities folder.

Sid Kirchheimer writes about health and consumer issues.