[drzaiusx11]

"Copy protections" back in the day often looked for fixed strings in seemingly random places. In the worst cases, this even went outside the machine's memory addresses. Several programs I had would farm this task out to the users and ask for specific words from specific pages in manuals on particular lines. I had to hex dump the binary's lookup tables to even get older software to run many a time ;-)

[justin66]

I'm not sure why copy protection came up on this thread but when it came to the Apple II, one of the more effective methods was to intentionally include a damaged or unreadable sector at a predictable place on the software's floppy. A standard copy would bomb out on one of these disks, but of course special copy software could do something with a disk like that.