1984, Jet Set Willy was released. A great game that every kid at school wanted. Of course we all wanted a copy, but it cost £8 here in the UK, which was several weeks' pocket money.
Copying games then involved finding a kid whose Dad was seriously into Hifi and had a stackable stereo system, then we'd copy it with their tape to tape system. But JSW had this as the cassette inlay.
How this works? When the game loaded after about 10-15 minutes, it would ask what colours were in Grid square A5, or H9 etc. Get it wrong twice and the game would exit and you'd need to start over.
(If you're wondering what happens if you're colour blind - you could write to the publishers and if they accepted your complaint, they would ask you to send them the game and would give you a cheque to cover the refund)
Of course, kids are determined and inventive, and this was well before photocopiers or digital cameras, so we would spend our lunchtimes with pencil and paper writing down every single combination...
It was a good game, with some great music, but really really hard.
(Credit to https://intarch.ac.uk/journal/issue45/2/1.html for the picture, and the page also goes into more depth)
Dungeon Master was distributed on a floppy disk that had a specific weak sector that would randomly return 1 or 0 when read. The game would periodically read that sector and, if it returned the same bit x times in a row, it would kill your entire party. When copying the disk, the original would read either 1 or 0 and then write that value in that specific sector, meaning the copy would always return 1 or 0.
The check was random, hidden in graphics files, and this, combined with some obfuscation and some more copy protection, meant it took over a year for the game to get cracked. A record at the time.
The dev claimed that the time and effort spent on the protection scheme was worth it as it allowed the game to keep selling through typical sales channels for much longer than usual.