Upgrading to a new and better computer? Donating, selling or trading in your old one? When you trade an old one for a new one, be sure you don't trade your personal information along with it. Before letting an old computer go, it's important to delete personal files. Merely dragging them to the trash won't work because copies remain hidden on the hard drive, and devious "experts" can retrieve them. In a recent experiment by MIT of 200 old computers, 70 gave up files -- things like bank and medical records and more than 5,000 credit card and PIN numbers. So, before you let your old computer (and info) go, purchase special software that "scrubs" your drive or call in an expert. They recommend "overwriting" at least once, and maybe several times. For good ideas and sources, enter "secure delete" in a mainstream search engine (like Google). For more tips, visit our Web site at onthehouse.com. And that's the On The House tip for today.