Keygen....where the user can download a key from some cracker site and download your game from your website using up the bandwidth. or Demos with only 2 levels, the user have to download the full version once he pays up....but he can download the full version game from a site like...Limewire?

You could make the keys based on some algorithm so a random keygen would not work.

You could use a protection system to help prevent this (see this for a sample one with source)

You could put fake keys out on the internet and when someone tries to register that key display a message like: "You have entered a cracked key and your information has been sent to our company. Please make a payment in 30 days or your information will be sent to the proper authorities."

There are a lot of things you could do.

I'd say a mix of both.

They have to download a full version, but its encrypted using there computers hardware as a key.

Still can be hacked, but it requires more hacking. (esp if you add many, many different checks).

From,
Nice coder

There is actually a balance between two issues to consider. The strength of protection vs the ease of use for the customer. The more extreme your protection the more hassle for the (honest) user to the point where it starts to put them off. Some of the existing software protection systems mean that you can't run a game on a machine that has particular CD burning software. While that is designed to hamper copying it actually impacts on all your honest customers as it is virtually impossible these days to buy a machine that does not have a burner and some form of burning software as standard.

Many shareware developers feel that making the user download a demo then have to download a full version again discourages sales. They believe it should be as easy as possible to buy the game by just paying online and having the demo enabled into a full game.

Thanks!

I have a separate full version for my shareware game.
No problems with this so far.

By the way: Even big casual games sites like Realarcade don't care too much about copy protection. So you'd better concentrate on finishing your game instead of thinking about sophisticated protection methods.

Check out this Anticracking FAQ for some tips on preventing easy cracking of your software.