Serial codes for shareware programs are useless. Its trivial to get a hacked serial number that works for practically any shareware game on the web.
The way forward is to keep your download over 5MB, and have a separate full and demo version. Makes ure there are some data differences too, so people cant just host a small full version .exe file.
This way hackers have to pay the bandwidth costs of hosting a 5MB file, and they just don't do that.
I'm getting into the desert rats game now. Its quite hard, but good fun.
Been working hard on the movies, and doing bits and bobs on Government. I need to pick a better name for that game...