So I'm selling my old iBook and I want to format the hard drive so that the old data cannot be recovered. The simplest solution is to boot from the original OS X CD and Erase Disk. But I'm guessing that this process doesn't actually write over all the old data. So should I use a different app to write zeros or patterns to the disk first? I've read only a little about this, but I'm definitely a beginner on this topic. Has anyone done this, and if so, what's a good app? Is data easily recovered from an erased hard disk? Any thoughts would be appreciated.