If you’re selling (or giving away) a computer, just deleting your old files isn’t good enough—they’re still there on your hard drive until the computer needs that space for something else. It doesn’t matter if your computer is going to someone you trust—should that person pick up the “right” virus, any of your confidential personal info/photos still on the hard drive will be “gone, baby, gone."
How do you protect yourself? Use a program like Eraser or Permanent Eraser to really wipe that computer clean before it leaves your possession:
Permanent Eraser (Mac)