What can survive a secure erase and reinstall? Something did ... how is that possible?
I have encountered something completely puzzling to me.
I recently purchased a used iMac from a reputable vendor who did a fresh install of Catalina. They must have used or tested the unit on their own WIFI network before shipping, because it appeared in the list of WIFI networks in System Preferences > Network > WIFI > Advanced > WIFI Preferred Networks. I deleted the network from the list of Preferred Networks and then clicked Apply. The network was gone and should have been gone for good at that point.
After that, as part of my overall process of setting up a newly-acquired used Mac, I booted into Recovery Mode and did a 2-pass secure erase of the entire HDD and then reinstalled Catalina. The erase and reinstall were both successful.
After the installation finished and I got through all the initial Apple setup screens, I went back to System Preferences to check various settings ... and in WIFI Preferred Networks, the vendor's WIFI network showed up again!
How could this be? I deleted the network from Preferred Networks ... and then did a 2-pass secure erase of the entire disk and reinstalled Catalina. How could this entry in Preferred Networks survive all that?
I can delete the network entry again ... but how is it even possible that it survived a secure wipe & reinstall? ... and it raises the question of what else could be lurking in a way that could survive a wipe & reinstall?
ps. If it's helpful to know, it's a 27" iMac 17,1 MK462LL/A with an HDD - no SSD or Fusion drive.
iMac Line (2012 and Later)
