Did you know that even after you've emptied your Mac's trash can, the data still has not been permanently removed from your system? Anyone who knew where to look could easily unearth this data. You can prevent this by using the secure empty trash option on your Mac. Whenever you put something in the trash, instead of pressing delete, go into 'finder' up top and press 'secure empty trash'. What this will do is replace the data that is left behind on your hard drive with random ones and zeros. If that is not enough go, into the disk utility option and then select your hard drive. From there go to 'erase' and select 'erase free space'. What this does is go around all the free space on the hard drive and replace each one and zero with a zero. You can select from three options: a single pass, seven passes or even thirty five passes. Each variation takes more time than the one before it. This will keep your data secure from prying eyes.