Hi there,
I also had to prep my laptop before it was sent back to HQ. Here is the Apple article that I used. It is pretty good in that it remains you of some good stuff – like de-authorize in the Apple Store. When it got to the point to erase my drive and wipe it I was not able to use the Security Options button as it was grayed out – so I could only erase it. So I used SystemRescue CD to boot and truly make this disk wiped well.
BTW, I booted to the Recovery Mode (Command + R) to wipe the disk, and to a USB version of El Capitan and in both cases was not able to select the Security Options. Now, as I write this I find an article that could have let me wipe nicely without SystemRescue.
Also, I had planned to put OS X El Capitan back on the laptop so it was ready for HQ to work with. It seems that you cannot do that any longer without a Store Account and I was concerned if I did that it might cache it somehow.
BTW, I do like the Ultimate Boot CD for the range of disk wipe and other tools. Very handy.
But it is ready now.
Michael
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Notes from MWhite 