This is worth reading (it’s not too long and there are a few key steps worth understanding, especially when it comes to wiping your Mac) and bookmarking.
How to wipe your Mac, Watch, iPhone or iPad ready for selling
This is worth reading (it’s not too long and there are a few key steps worth understanding, especially when it comes to wiping your Mac) and bookmarking.
Except it’s wrong about erasing your Mac. You can still securely erase a volume in El Cap. Click on the volume you’re erasing, click Erase, Click Security Options, choose whatever level you feel comfy with.
Rather obviously to erase the boot volume you need to boot from something else (a cloned disk, Recovery, etc) but… that’s always been true.
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Personally, I wouldn’t trust my critical data to a simple build-in data erase function. I’ve heard horror stories from folks who went for self-comforting option and highly regretted it. You get what you pay for.
Eraser Software from giveumore.com is good choice.