A nice new technical post from Chris ‘scarybeasts’ about the arms race of floppy disk copy protection schemes, mostly from an Acorn perspective:
Many good links within.
‘scruss’ on Stardot adds:
Weak Bits were a really big thing on the Apple II, going back to 1982 or before. It’s worth checking some of the 4am crack logs (like this one: The Kingdom of Facts) for the details. It seems that Datasoft did it with a modified C64 drive attached to an Apple II.