I bought a MBP 2018 off ebay.

When I boot up the machine it showed the install prompt for Big Sur. I imagine the person who owned it before reset it such that it was ready for re-installation.

My first question is, how sure can I be at this point that there is no malware on the machine?

I went through the installer and then I downloaded Monterey via the app store. I put Monterey on a usb drive and made that drive bootable.

If I can't be sure of the first question, if I install Monterey via the usb drive that I created using the os I am unsure about, can I be sure the bootable usb drive that has Monterey is ok?

Thank you!

1 Answer 1


Boot from your USB, then use Disk Utility to Erase the existing Volume, after that you can re-install mac OS. Anything the previous owner would have installed would be wiped this way.

If you want to go the extra mile use another machine to create the bootable installer or use Internet Recovery (boot with Option-Command-R).

  • This was my thought too... would you go the extra mile or consider it unlikely the bootable usb created via the questionable machine should be ok? I am just not familiar enough with what safeguards macos has in place to ensure a legit os is installed. I don't have any other macos machines so I would need to create it from a windows machine. Commented Nov 18, 2021 at 3:11
  • 1
    Since your MacBook has a T2 chip you have the option to only allow signed operating systems trusted by Apple: support.apple.com/en-us/HT208198 - AFAIK there are no known vulnerabilities that would allow a compromised OS to be installed. Commented Nov 18, 2021 at 13:55

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