I remember that on either the Vic 20 or the Commodore 64. With both the Vic and C64 you could use game cartridges as well as tape drives. I seem to recall one of the tape cassette games used a plug in one of the external ports to prevent copying. Nobody was able to copy the cartridges, but the cassettes could almost all be copied on your home stereo system. (If you played the cassette on your stereo, you would just hear a bunch of whistles and clicks like when pick up the phone while using your old 2400 baud modem!)

I guess Settlers III beats everything else with iron smelters creating pigs
(especially since that wasn't a problem only pirates had to cope with XD)

Aaargh.....

Lenslok....

Elite on ZX Spectrum.....

I'm gonna have nightmares all over again, after 25 years of peace.....thanks guys...

happy to help

Psi 5 Trading company (for C-64) wasn't a very easy game to learn. Partly because it was indeed a difficult game, and partly because the manual was printed in a very tiny blue type on a big dark blue poster with some space image background muddling up things! Impossible to copy with a copying machine, yes. Also just about impossible to read without a very bright light and a magnifying glass.