This protection works by checking for a series of bytes on a track (or tracks) that has no sync marks or standard sectors of any kind. This is impossible to copy with serial nibblers, but a program can be written to run in the drive to recreate these tracks since the patterns are known. It is no problem to reproduce them in MNIB, or any other parallel or extra RAM nibbler.

Reading these tracks in MNIB gives you only a very small chance of getting a working image for emulators due to lack of sync/framing on the protection track. All images will work copied back onto a real 1541, because the 1541 acts on a raw bitstream instead of whole bytes like current emulators so the bitshift does not matter. Because of the way the drive attempts to lock onto sync, typically track 2 needs to be shifted two bits to the right to make a an image work on emulation with the protection intact.

There are two versions out in the wild that I have run across.

Version 1: Checks for the pattern $eb $d7 $aa $55 on track 37, then checks for the pattern $d7 $d7 $eb $cc $ad on track 36. This is actually a tougher protection than the latter, so I'm not sure why it was changed. If the byte patterns are not detected, it forces the drive heads onto (or beyond, were it possible) track 42, like copied Rapidlok disks. This can jam drives and require service, so perhaps that's why they toned it down. :)

Version 2: Checks for the pattern $D7 $D7 $EB $CC $AD on track 2. It is actually a simpler form of the earlier protection scheme.