Mm, it didn't take all that long to crack, when I did it for fun. My patched version of Mon had a reference search, and the code in the graphics.dat stuck out because I was single-stepping from interesting places. That trick makes deadlisting harder, but live debugging there's no real difference.

Side note: it kept the XBIOS/GEMDOS keyboard/mouse drivers in place, tried to unlink a debugger and wipe the RAM - but it forgot to patch out the good old Alt-Help "screen print" vector! So if you hide a routine in low memory, just above the vector tables, but below where it wiped, around $200-$400 ish from memory… <g> (Oh, and a Syncro Express would just duplicate the thing cold, even on Express mode, but that's no fun~!)

Chaos Strikes Back was bloody difficult as a game! Wonderful work, all around, it's a masterpiece. I bought more than one copy (and actually played Dungeon Master after CSB). I never did finish CSB!

On a similar thematic note, the later, futuristic first-person dungeon crawler Captive has much more interesting copy protection; the author (ratt) wrote his own disk routines (internally called RATTDOS). That was a tough one. It's very Amiga-ified inside, so I wouldn't be surprised if the Atari version shared most of the code. It has procedurally-generated levels, although I think it may be impossible to complete after a certain point.

The Atari ST version of Sid Meier's Civilization is also well worth checking out as a historian; it was written in C, and they left all the debugging symbols in! Fascinating; you can see the original "nuke-happy Gandhi" bug underflow first-hand, and the world maps were really just planar bitmaps, so when you'd figured out how they were stored, it wasn't hard to knock up an editor.

I also have fond memories of Wayne Smithson's Anarchy and its disk's Rob Northen exotic copy-protection's space-filling rant, although I suppose there are only a few people who even know what I mean about that. If you can find an original copy intact anywhere, break out a sector editor, and start reading. The format gets harder the further on in the disk you go. :)

To the person below who had trouble with Elite II: Frontier - um, perhaps your platform was harder? The executable we all seemed to have on the Atari was standalone, was one $4E75 RTS away from skipping the manual protection, and had absolutely no checksums in it at all (to my immense glee - I had lots of fun modding it)! I'm having some fun downtime playing its recently-released sequel Elite: Dangerous, too - but that's online, so of course I'm playing clean! (I did test a couple of cheats during the alpha, and reported to help the devs patch some of the most obvious gamebreakers.)

Other than online stuff, I honestly don't think they've discovered any particularly new tricks since those days. There's a lot of lost gems that get reinvented. The very best, newest, "anti-tamper" techniques are essentially, just bits of obfuscated code interleaved with checksums. Underwhelming, really. It boggles my mind that people still do that stuff - just make it easier to buy games, and it's hard to get easier than Steam! (My opinion of the "strong" obfuscation technique that bloats simple 32-condition IF statements to multi-gigabyte sizes is also pretty poor, as it stands at the moment, although the state-of-the-art could always improve.)