A recent study of hard drives purchased on eBay found that 42 percent of them contained data, even though the sellers claimed that they'd been formatted to prevent that from happening. It's a good reminder: You need to do more than format hard drives before you sell, give away, or destroy your old PC. The study was conducted by Blancco, a company that provides hard drive and SSD format tools. It was obviously set up to encourage users to download the company's tools and services. But...