Several years back there was advertising related to the software which would entirely wipe out hard disks with the technique accepted by the U.S. government by writing 0s and 1s on the drive in numerous protocols? And does still software available in the market and yes it exists for Macintosh (PowerPC and Intel).

Such software are available in the market for free of charge and it is already existing in the Mac computers if you are using operating system like Tiger or Leopard and you want to locate the program you have to go through following steps like Launch Disk Utility (/Applications/Utilities) and when the program unlocked select the particular drive which you want to completely wipe out in the pane which is on the left hand side of the Disk Utility window dialogue box. Click on the Erase tab and after that click on the Security Options button which are listed at the bottom of the dialogue box. And a sheet will be displayed showing four options. Don't Erase Data, Zero out Data, 7-Pass Erase, and 35-Pass Erase.

The Don't Erase Data option:

The name itself implies not to wipe out any data from the drive but it will wipe out your directory and confirm Mac were your data is being stored by use of any other open source software you can recover your data after you’ve employed this option so it is not an secured option.

Zero Out Data:

Which note down zeros over your drive one time. It's not up to command standards, but recovering data from this drive would be a task.

7-Pass Erase:

Which meets that US Department of Defense 5220-22 M standard about which you've heard so many good things. It engraves over your data seven times.
And for the truly anxious, there's the 35-Pass Erase option, which, as the name mentioned, it note down junk over your drive 35 times. If you want your data super-mega-ultra-really gone, this is the one to use.

Kindly Note that the 7-pass option takes seven times longer to overwrite your data as compared to other than the Zero out Data option. Similarly, the 35-Pass option takes 35 times as long.

If even this selection leaves you with a slight case of the Jim-jams, let me suggest the Multi-Pass Sledgehammer option. If you need your data to be entirely unrecoverable and if you are willing to give up a hard drive to make this happen, extract the drive from your Mac, take it out back.