[KaiserPro]

a previous company I worked for spent many pound coins on using metafortress to make our softeare exceptionally difficult to crack.

It went from 5 minutes in a hex editor to being a rather involved job. So it stopped it for a while.

Then people realised that instead of cracking licensed program, it was much more simple to crack the license server. (this also made detection much harder.) It also had the advantage of allowing rafts of other software not made by us work as well.