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The only sure way is to reformat and zero the drive and then re-install the operating system.
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The only sure way is to reformat and zero the drive and then re-install the operating system.

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Buy a new HD of same size and swap the old disk. Format the new disk and install a system on it. That way you keep everything and you can find the disk something else to do.
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Buy a new HD of same size and swap the old disk. Format the new disk and install a system on it. That way you keep everything and you can find the disk something else to do.

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I have to return my MacBook which I have had for three years. How do I make sure all my personal usernames &amp;&nbsp;passwords are no longer saved anywhere ?<br />
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Also, any recommendations on other things I should do to make sure all my personal data is removed? &nbsp;Reinstalling the MAC OS is not an option.
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I have to return my MacBook which I have had for three years. How do I make sure all my personal usernames & passwords are no longer saved anywhere ?

Also, any recommendations on other things I should do to make sure all my personal data is removed?  Reinstalling the MAC OS is not an option.

MacBook - Delete All Personal Information

Mac OS X is the desktop operating system from Apple Inc., found on Macintosh computers. OS X consists of a Mach/BSD-based kernel, operating system interfaces primarily based on FreeBSD and additional frameworks (written in C, C++ and Objective-C providing user interface and application-level services.