|Tip 6||Get Rid of Files—Securely|
Whenever you empty the trash, the files are deleted in the standard way; that is, the OS X filesystem makes the space they occupied available for another use. However, the actual content of the files sticks around on the disk until it’s overwritten, and it can be recovered using one of the many third-party file recovery tools available.
To avoid this, you can securely empty the trash, which involves writing over the data with zeroes so that it can’t be recovered (at least outside of a high-tech crime lab), but bear in mind that the files might still exist in your Time Machine backup (see Tip 307, Make Time Machine Forget a File).
Note that if your Mac has a solid-state hard disk (SSD), such as those fitted ...