You can't just rely upon deleting your files, because security experts say the stuff is recoverable by a sophisticated data thief. In fact, traces of data may remain, even if your repartition and reformat the drive. That's why you should use one of the numerous software programs designed to obliterate your information, such as Darik's Boot and Nuke (DBAN), DriveScrubber, or Lavasoft File Shredder. The latter has the advantage of allowing you to wipe out sensitive data but leave other stuff that doesn't put you at risk [source: Lamb].
With a Mac, this process is easier. Just boot up your computer from the recovery partition by holding down the command and R keys as it restarts. Then open Disk Utility. Under the Erase tab's security options, choose 7-Pass Erase, which will overwrite your data seven times, obliterating it. This is going to take several hours, so bring along your tablet and read an e-book or play Words With Friends [source: Arndt].