Security: The cleverest floppy disc protection ever? Western Security Ltd.
[ITRP] 3D0D: BCS $3CF7 It's not expected to be clear from this fragment alone (without all the subroutines), but what is going on here is a loop across tracks 1-8 inclusive. For each track, it is read fully and the length of the track is stored in a table at $3F71. Later, at PC $3CB6, these lengths are checked against a table located at $3D9B. The check is particularly interesting. For the copy protection to pass, a count is taken of each track length that falls within +-1 of the expectation, and this count must be 7 or 8. Immediately we see that this protection is not a precise technology. ...
Source: blogspot.com