If someone wants to know how the coding
principe   of   serial  number  of  the
Harlekin 3.1, here it is:

first  U enter 8 digits (ASCII) and put
them on some memory location and set A0
register  to  point at that, then enter
following prog  to calculate the rest 4
digits:

   move.l   #$1021,d1   ;main EOR value
l3 move.b   (a0)+,d2
   move.b   #8,d2
   eor.w d2,d1
   moveq    #7,d2
l2 tst.w    d1
   bmi.s    l1
   add.w    d1,d1
   dbf      d2,l2
   cmp.l    a0,a1
   bhi.s    l3
   move.w   d1,d0
   rts
l1 add.w    d1,d1
   eor.w    d0,d1
   dbf      d2,l2
   cmp.l    a0,a1
   bhi      l3
   move.w   d1,d0
   rts

And you'll get HEX value of the rest 4
digits.

One  of  possible  serial  number   for
Harlekin 3.1 is 12345678-9015.

This  was cracked by Dusan Dimitrijevic
from The Twilight Production! (TTP!) on
10th Februar 1994. Crackin' time 30 min