If you have sensitive data on your hard drive and you are worried about it being recovered, here is a simple way to securely dispose of your files. On Mac OS X, the secure trash option will delete your data 8 times for added security. To enable this option by default, simply open Finder Preferences by going to Finder > Preferences. Select this checkbox below:
If you only want to securely delete once, you have two other options. You can pull up Finder and click on Secure Empty Trash. Alternatively, you can hold down CMD and right-click on your trash bin to select the option to securely delete. The reason why you might want to do this is because secure empty trash is a slow operation that must write and rewrite data 8 times. This process can be quite slow and most of the time you will not need this much security. Therefore, you should select one of the options listed above to complete this operation on a one time basis.