"Market" for old macs?

[Gordon JC Pearce]

Jim Leonard wrote:

> But I agree with you that some DOS-based games were so trivial that they 
> could be cracked with a hex editor and not a debugger.  For example, 

I do remember the incredible feeling of achievement when I cracked the 
copy protection scheme on the cassette version of Jet Set Willy on the 
ZX Spectrum.  For those who don't remember, it used coloured boxes in a 
complicated grid to give you a code - it would display "Please enter the 
code at location A5" and you'd look it up, and type in "3241" or 
whatever the colours were.

In this case I used MERGE to get the loader to load but not run (common 
trick) and looked at where it jumped off into the machine code.  Then I 
traced it through, using the Z80 opcodes in the back of the very 
stunningy fine manual, jotting it down, NOPing out a bit here, sticking 
a RET in there (crude breakpoints), until I discovered - there was 
nothing terribly clever going on, once it got a code it was happy with 
it just jumped to another address.  No decryption, no magic stack 
contents (the last thing it did before jumping off was reset the stack 
pointer), nothing.

Change the address in the loader's RANDOMISE USR <wherever> line, and 
the game started up with no need for the code!  Woohoo!  So then I 
copied it onto a ZX Microdrive cart and I was set...

I must have been about 13 or 14 at the time.  I'm still pretty proud of 
it, really, my first real crack...

Gordon.